My List: (in no particular order)
1) Gnomes that have a decent paint job!!!
2) Gem dragons
3) Stirges
4) Vermin swarms (A whole bunch of tiny, a whole lot of trouble)
5) Driders
6) Giants (of all types)
7) Vampire
8) Bears (and not celestials or fiendish)
9) Mounted figures (Fighters are great and all but a Paly needs a horse!)
10) More lizardfolk poses
11) More Draconians
12) Hydra
13) Female gnomes (so far all they have made are males so this is different than #1)
14) Ankheg
15) Cloaker
16) More goblinoids
17) Scorpions
18) Centaurs
19) Black Scale lizardfolk
20) Aboleth
Siege weapons, treasure, dungeon dressing would be awesome, but I don't see it happening, all of those already exist and don't really support a minis battle format (ok seige weapons do, but they would already have crew figs attached or worse the weapons are VR and the crews are all C.)