Each year I have taken a different army: Plague Marines, then Vanilla Marines, then Tau last year. Here are the lists I am considering to take this year. The event is heavily comped, but that is panel comp so you get a fair score for your list, not an unfair score from a losing opponent. So bear in mind I'm trying to make lists that are interesting and fit to a theme, but still competitive.
Vulkan Drop Pod 750
Vulkan H'estan (175)
Dreadnought - multi-melta, heavy flamer, drop pod (150)
Tactical Squad - multi-melta, melta, combi-melta, pod (220)
Tactical Squad - multi-melta, flamer, pod (205)
Drop in first turn with devastating twin-linked melta alpha-strike. Dread, tactical squad and Vulkan attempt to cover each other's weaknesses. Second tactical squad drops in a later turn near an important objective. Pod positioning is critical as all weapons are relatively short ranged and there is no other mobility.
Draigo Wing 750
5 Paladins - 2 MC psycannons, 2 MC halberds, 2 MC hammers, apothecary (415)
1 Paladin - MC hammer (60)
Only 7 models on the table but what fine models they are. The big squad has 8 psycannon shots, 2+ save, Feel No Pain and 2 wounds, whilst Draigo protects the squad against Strength 8+ attacks (he even gets FNP against missiles!). Draigo can keep the single Paladin in reserves with Psychic Communion until turn 4 easily., when he drops in for Holocaust and a late objective grab. Biggest weakness will be flexibility as it's basically one unit.
Tau Mech 750
Shas'el - missile pod, black sun filter, drone controller 65
2 x 6 Fire Warriors - devilfish with multitracker, disruption pod (310)
Piranha - fusion gun, disruption pod (65)
2 x Hammerhead - railgun, multitracker, disruption pod (310)
Something different, inspired by a list I found on Yes The Truth Hurts. Hard to kill but very reliant on the two railguns to lay down hurt. 5 disruption podded vehicles is nothing to sneeze at. I have no idea if this would actually be effective, because it lacks any substantial damage output. Probably plays like slow Mech Eldar.
Nurgle Mech 745
Daemon Prince - mark of Nurgle, wings (150)
Dreadnought - auto-cannon (110)
2 x 5 Plague Marines - 2 meltas, rhino (340)
Vindicator - daemonic possession (145)
The Dreadnought was a concession to comp - otherwise I would drop daemonic possession and take a second Vindicator, but I know that would get marked harshly when combined with such good troops.
This list is still effective, if the Dreadnought doesn't mess you over and the Vindicator survives long enough to drop a shell or two. Note that there are 5 targets for anti-tank fire (counting the Prince) and nothing that cares about bolters :)
Imperial Guard Tank Company 745
Company Command Squad - 3 meltas, chimera with multi-laser, heavy flamer (135)
Veteran Squad - 3 meltas, chimera with multi-laser, heavy flamer (155)
Veteran Squad - 3 grenade launchers guns, chimera with multi-laser, heavy flamer (140)
Leman Russ Battle Tank - heavy bolter (150)
Leman Russ Demolisher - heavy flamer (165)
Well I am currently in the middle of negotiations to pick up five Leman Russes, so this might well be the small version of my next army. See here for my initial thoughts on building a Tank Company (and building tanks our of card!). Its an attempt to build a traditional Leman Russ Platoon with armoured support. The psyker rides with the plasma squad as his power complements their range. Lots of dakka and might have difficulty contesting, so it should make for violent and tactical games. Bit worried about the knee-jerk comp score it will attract though...
Space Wolf Mech 746
Rune Priest - Jaws, Lightning (100)
2 x Wolf Guard - powerfist, combi-melta (86)
7 Grey Hunters - 1 melta, banner, rhino (155)
6 Grey Hunters - 1 melta, banner, rhino (140)
5 Grey Hunters - flamer (75)
5 Long Fangs - 4 missiles, razorback, las/plas (190)
Plain old Rhino spam with the overpowered marine codex of the moment. Long Fangs get the Razorback so they can deploy up to 14" in on dawn of war - then hand it to the 5 marine Grey Hunter squad. Tactics? Move forward, assault and kill stuff. Or stay back, shoot, counterattack and kill stuff.
So there you have it. What should I take to Judgement Day this year? Any minor tweaks you would make?