Since there have been many, many changes since the last codex, I felt like we needed a new tactica to represent the new units and by extension the new strategies the Tyranid race now has at its disposal. Not being a particularly senior 'Nid player myself I probably won't be contributing much personally, but I'm sure the old hands will quickly learn the tricks of the trade and pass them on. Anyway, I'll get the ball rolling with my Tyranid Warrior tactica! Behold!

Tyranid Warriors

These guys, now being a Troops choice, occupy a vastly different position than in previous editions. Since the revamp of the objective capturing rules these guys also play a vital role in helping you secure victory in 2/3s of the missions you'll be playing. Not to say that they won't be useful in Annihilation that is, just that in Objective missions their role is perhaps more emphasized. There are two basic ways you can run your Warriors, depending on the battlefield role you want them to play. I've annotated these two types below.

Striker: These are your assassins, your "strike force" if you will. This means you want your Warriors to be taking out the important stuff in your opponent's army, for example Generals, units consisting of multi-wound models (Nobz squads, Ogryn units, etc etc) which are often your opponent's "heavy hitters", the dudes you really want to take out. Equip your Warriors with either dual Boneswords or a Lash-Whip and Bonesword, depending on how many points you can expend. The dual boneswords will, if you wound the enemy, most often result in that same model failing it's Ld test and dying immediately. This is because the average of 3d6 is 10.5, which is higher than even the highest Ld value in the game. The lash whips are less recommended, although they reduce the opponent's I value, because Warriors have such a high I value anyway, this is rarely useful unless you're facing those damn Space Elves.
As to the Adrenal Glands/Toxin Sacs choice, for me it comes down to whether you'll need your Warriors to destroy light vehicles or tough creatures. Adrenal Glands for the light vehicles (and Basilisks!), Toxin Sacs for facing other Tyranids, most Space Marine armies, Daemons, etc etc.
I'd usually mount these dudes in a Mycetic Spore, since being primarily CC based (unless you didn't replace the devourers with scything talons, which is what I'd recommend. I roll a lot of 1s and even a single pair of STs is a big bonus, especially since you'll usually be hitting on 3s, in which case you'd only be without a re-roll on a 2!) you'd want to get into combat ASAP. Walking across the table exposes them to ranged fire and other nasties.

Defender: These guys are used to camp on objectives, firing on all those who dare oppose them. I'd give these guys a Barbed Strangler and/or a Venom Cannon, with the remaining Warriors in the squad with Devourers. What you do, see, is shoot them with both the Strangler and the Devourer, so the opponent gets a -1 to his subsequent pinning test. A nice little combo which someone suggested on another thread. I'd also consider giving them either rending claws or boneswords to dissuade anyone trying to assault them. These guys are very resilient if you plant them in cover, shooting out at anyone who may be threatening them. They get cover saves against anything that pierces their usual armour, and 3 wounds apiece means they aren't going anywhere fast.

Comparisons to other units which perform the same function:
Striker: Tyranids truly have a wealth of options when it comes to really getting stuck into close combat, so the "Striker" build may not seem that useful. However, if you look closer, you'll see that a lot of the real CC monsters are also quite expensive. Carnifexes can destroy everything in their path, but run you up about 200pts for a CC-dedicated unit. Hive Tyrants are similarly expensive, running over 200pts for a Winged variant. Trygons are the same, same for Mawlocs, etc etc etc you get the idea. Now, for a 3-Warrior brood with dual boneswords will run you 135pts. Plug them in a Spore and that obviously increases, but still not beyond that which a 9-wound, deep striking, armour-ignoring, instant-deathing unit is worth. This unit will almost always eradicate most units in its path, be they CC specialists or not. Multi-wounds our specialty!

Defender: For ultimate objective-grabbing campy goodness, you can't really go past a Tervigon taken as a Troops choice. Put it on an objective and watch as it spawns a literal tonne of ablative wounds your opponent will need to chew through. Not only that, but these same spawned units can go adventuring off by themselves and claim their own objectives! Our little Termagants are growing up! *sniff*. However, once again this unit will be quite expensive, since you need to both get a unit of termagants first and then the tervigon in order for it to be a Troops choice, which all up will run up about 210pts naked, and with the smallest 'Gant unit you can get. Compare the 4-strong Warrior brood with a Barbed strangler and devourers, which will only be 130pts all told. Add in some rending claws to discourage assaults and you have a nice round 150pts. This unit will need dedicated fire to remove effectively, and with a Ld of 10 it won't be running anywhere either. Also, any unit that can fire at you will most likely be in your firing line as well, and since they probably won't be as well-protected, you can remove them from the equation pretty easily.

So there you go, I hope other people add to this to make the best Tyranid Tactica possible.