Theme collection

Update (24.03.2011): There is a much more up-to-date list here with all the new themes.

Here's a list of some of the existing themes around:

2.1:

Dark10 by Chewitt
X10 Res Mods by XperiaX10iUser
ElementaL by Mr_Element
Pitch Black by Shukla
Xdre4m by PoTi_96
PGFX™ Eternity by SEMPITERNAL
Transparent Status Bar Theme by thefunkaygibbon
HTC Sense and Stock Android Status Bar by dk2000zx
Enigma by Mobzter

1.6:
Dark10 by Chewitt
Frankendroid by Bazza1976
Enigma by Mobzter
Red Theme by djsystem

There's also a lot more here thanks to gavriel18

If I have missed any please PM me or post here and I'll update the list. I just scanned the first 3 pages in the forum.