After discussion with other Warseer members and Mods, I have come up with the following Summary which I think fairly describes the rumour situation without entertaining wishlisting and supposition.
It is not my intention to imply that only these rumours may be discussed, only that these are the ones I have determined to be strong enough to put in a summary.
People should feel free to post and discuss anything that they hear, regardless of the source, but the Summary will only ever include those rumours which I feel deserve to be here.
[SIZE="4"]General info[/SIZE]
Release 16 January 2010
Written by Robin Cruddace (author of IG Codex) and is 96 pages long.
Phil Kelly has also said we can expect to see "4 new species never seen before in a codex, one dwarfing the Carnifex." Most solid sources agree this large species is likely the Trygon.
The Incoming Tyranids article on the GW website makes mention of new Tyranid Species.
Codex Cover – Art by Adrian Smith
http://www.warseer.com/forums/attachm…29&d=1254136277
Box art background:
http://www.warseer.com/forums/attachm…09&d=1254475533
http://www.warseer.com/forums/attachm…08&d=1254475499
Studio army will be in Hive Fleet Leviathan painting scheme with red weapons (as on cover and new box art).
A full summary list has been posted on the internet, but it includes far too many large creatures and has been generally dismissed as fake or wishlisting.
[SIZE="4"]Rules[/SIZE]
Army-wide Special Rules and Biomorphs
Reds8n has said we can expect to see many new and improved psychic abilities in the book.
Whisperings that Biomorph effects will be changed somehow. Nothing solid on this.
Stickmonkey tells us the Lash whip may be changed to be able to target specific models in close combat.
Stickmonkey also tells us Crushing Claws may change to Dreadnaught CCW plus an additional new ability.
This may seem odd, but they could be available on more models than just Carnifexes, plus there could be other changes to Carnifexes that make this change relevant.
Special characters including Old One Eye are rumoured to return. Phil Kelly explained that they are not meant to be individuals, but more like mutated survivors from a big war. Robin Cruddace has supposedly said they may give special rules to the whole army.
Phil Kelly has implied the Tyranids will get an increased anti-tank capability
*Note, FOC slots are representative only until more solid rumours appear*
HQ
Hive Tyrant – Stickmonkey tells us Tyrants are likely to get more psychic powers along with possible increases to Attacks and Initiative and a 5+inv save as default. He also says there is a chance at an expensive regenerate option for the Tyrant as per the Carnifex.
Tyrant Guard – No news yet
Broodlord – Early rumours of the Broodlord allowing Elite Genestealers as Troops.
Elites
Tyranid Warriors - There may be a greater emphasis on Tyranid Warriors, perhaps even allowing you to take them in every FOC slot. For example if they have wings then they're Fast Attack, Tougher/Stronger and heavy weapons make them Heavy Support etc.
Lictor – Some speculation the Lictor will get a fix to Deep Striking into Terrain. Nothing solid as yet. Stickmonkey tells us they may get a deployment alternative to Deep Strike.
Troops
Genestealers – There have been vague rumours that Genestealers may be moved to Elites, with Broodlords allowing them as Troops
Gaunts – No news yet
Ripper Swarm – No news yet
Fast Attack
Gargoyles – Vague rumours that Gargoyles may see a minimal increase to Initiative. May also get access to (altered) Biomorphs.
Raveners – Stickmonkey tells us they may get a deployment alternative to Deep Strike.
Spore Mines – No news yet
Heavy Support
Carnifex – At GD Italy, Allessio supposedly said, "The new book will let players field even more Carnifexes than before" No further news on what this may mean. Stickmonkey tells us there may be significant changes to the Carnifex, but that they will “make sense” and people will still want to field many of them.
Biovore – No news yet
Zoanthrope – No news yet
New Species
Trygon - Rumoured to appear in the Codex or at least as an Apocalypse sized plastic kit. Rumoured to have more head and tail options. Raveners rumoured to retain the ability to Deep Strike through the same tunnel as the Trygon without rolling for Reserves and may also be able to Assault afterwards. Has a variant called the Mawloc.
Venomthrope - Reds8n's early mention of a "psychic variant of the Lictor" seems to be based purely on the feeder tendrils of the new Venomthrope (Toxathrope in German). It appears to have 4 lashwhips, possibly toxic sacs similar to a Malanthrope, and is rumoured to be a psyker.
Pyrovore – Possibly a new Biovore variant with Pyro Acid spray weapon mentioned by Reds8n. Alessio also said at GD Italy, "I would expect something similar to a Tyranid Basilisk, a new species with a brand new metal model is likely" which could cover this.
[SIZE="1"]*Note - Alessio was talking about the IG Tank called a Basilisk, and not the Mythical creature.[/SIZE]
Hive Guard – New species similar to Tyrant Guard. Armed with a large ranged weapon similar to a huge Spike Rifle and some form of claws (rending or possibly crushing).
[SIZE="4"]Minis[/SIZE]
New boxes of Tyranid Warriors are starting to show up with the new Box Cover Art and repainted Warriors with red weapons (see below). The back features repainted versions of the other two Hive fleets, also with altered weapons. The red-turquoise Behemoth scheme now has black weapons, and the Kraken light brown-red has green weapons. Content of the Warrior box is the same.
http://www.warseer.com/forums/attachm…13&d=1256316512
http://www.warseer.com/forums/attachm…20&d=1257076227
Games workshop have said here that there will be 3 new Plastic kits and 3 new metal models released with the Codex.
Scryer in the Darkness tells us GW is playing silly-buggers with their release schedule, posting the following:
[SIZE="1"]*Note - the release dates on these have since shifted[/SIZE].
These would be the remaining codes we have as yet been unable to assign names to:
99060106064 <Tyranids metal blister code> £10.00 / US$16.50 / 13,00€ / Oz$28.00
99120106019 <Tyranids plastic box code> £30.00 / US$49.50 / 39,00€ / Oz$83.00
Best Guess is the "CENSORED" Release is the Trygon and the "CENSORED" (Direct Only) Release is a bits pack. This is yet to be confirmed.
Reds8n tells us the three Plastic kits are likely to be to be Trygon, Gargoyles and Ravenors. This has since been confirmed to me by a "cast iron source" 
Trygon (Plastic kit) – Alessio has been quoted as saying at GD Italy, "I cannot speak about the Trygon, but a hypothetical model would have the same detail and more versatility than the Skaven Doombell"
Mawloc variant has a distending mouth like the Red Terror and strange spines all over it.
The pictures below have been confirmed by Brimstone as resin masters of the kit, rather than the kit itself:
http://www.warseer.com/forums/attachm…22&d=1237931425
http://www.warseer.com/forums/attachm…21&d=1237931425
Gargoyles (10 plastic models) £18.00 / US$29.00 / 22,75€ / Oz$48.00 – Brimstone tells us Fleshborers are the only weapon option (or any other option) on the sprues and says each model consists of: Left wing, Right wing, Head, Left arm, Right arm with Fleshborer, main body with tail and half torso, other Torso half. I have been told they still come with flying bases (ie not sculpted scenic bases).
Brimstone has said they have long tails with some pointing up, some down and a couple curled. They have the standard three sets of limbs: weapon arms, wing arms, and small atrophied limbs at the base of the wing membrane.
Raveners (3 plastic models) £27.00 / US$44.50 / 35,00€ / Oz$74.00 – Brimstone tells us they will be 3 to a sprue. The kit comes with all Torso weapon options as well as an Emergence Hole marker.
Pyrovore (Metal box set) £20.00 / US$33.00 / 26,00€ / Oz$55.00 – Stickmonkey tells us it comes on a 60mm base and is somewhere between a Biovore and Canis Wolfborn in size.
Venomthrope (Metal Blister - 1 Model) £12.00 / US$20.00 / 17,50€ / Oz$33.00 – Shown in White Dwarf:
http://i735.photobucket.com/albums/ww354/g…Newcreature.jpg
Hive Guard (Metal Blister - 1 Model) £12.00 / US$20.00 / 17,50€ / Oz$33.00 – Stickmonkey tells us they come on a 40mmm base and are quite tall, solid minis, possibly prone to tipping. Silverstu describes them as looking like the current Tyrant Guard, but leaping forward and armed with a large ranged weapon similar to a huge Spike Rifle.
New Battleforce box £60.00 / US$105 / 85,00€ / Oz$165.00 – Contents remain unchanged. Independent retailer lists put release of the Battleforce at 5 December 2009 for some reason.
Hormagaunts and Termagants will be sold separately for £15.00 / US$24.75 / 19,50€ / Oz$41.00.
There was an alternate Brood Lord sculpt seen, but it is most likely just a test sculpt and will not be released with the Codex.
http://www.warseer.com/forums/attachm…47&d=1234737297
Jes Goodwin has said that a Plastic Hive Tyrant kit including all options was rumoured to have been considered. This is very unlikely to appear with the Codex. Alessio is rumoured to have said at Dames Day Italy, "If people want a new Hive Tyrant model will have to buy the Forgeworld one"
The Ripper Swarms that appear on the GW Website are from 2nd Edition, and have been there for some time. They are not new.
http://www.games-workshop.com/gws/catalog/pr…dId=prod1050159
Also die dünnen Einweghandschuhe, die z.B. bei Rettungsdiensten verwendet werden, behindern absolut nicht.