Here's what I've been running for the last few months.
HQ:
Hive Tyrant w/ Biomancy, TL BL devourers x2, Armored Shell, Tyrant Guard - 300
Hive Tyrant w/ Biomancy, TL BL devourers x2, Armored Shell, Tyrant Guard - 300
Elites:
2 Hive Guard - 100
Troops:
20 Termagants - 100
20 Termagants - 100
18 Termagants - 90
Tervigon w/ Toxin Sacs, Catalyst, Dominion, Stinger Salvo - 185
Tervigon w/ Toxin Sacs, Catalyst, Stinger Salvo - 185
Fast Attack:
4 Raveners w/ scything talons & rending claws - 140
I'm very pleased with the list's performance so far. Conventional Tyranid wisdom seems to be to never pay for Termagants, but they're so cheap, and provide some consistency to the spawned numbers that the Tervigons can put out. The Tervigons usually keep Catalyst and Dominion. While the Biomancy powers are great, they are also random, and the ability to give the Tyrants Feel No Pain is too good to leave to chance.
The Tyrants themselves are the lynchpins of the list. While only moderately effective in melee, they can shred infantry and medium AV vehicles at range, and are absurdly difficult to kill. Stacking cover, FnP, and possibly Iron Arm or Endurance can allow them to absorb an entire army's worth of shooting, especially if they haven't prepared for taking down this sort of target.
The Raveners were a late addition, but I've been pleasantly surprised with their performance. The rest of the list is fairly slow, and they add some ability to move across the board rapidly. Even better, they're one of the few Tyranid assault units that isn't completely screwed by terrain - while they still strike at Initiative 1 charging through it, they can move through it normally.
