theres really only a few different variations you'll see, they just LOOK very very different because a lot of roms come with built in skins and whatnot.

-sense UI vs non-sense UI
-homereplacement (adw launcher, launcherpro) vs stock android or sense.

check out launcherpro and adw at appbrain or any of a dozen other sites (google), and more examples can be seen at the xda eris dev site.

for example:
no sense, launcherpro home replacement
[ROM][GPL][10/4/2010] xtrROM4.6 [cache2cache,apps2sd,jit,lwp,oc,flash10] - xda-developers

senseUI
[ROM][GPL][10/4/2010] xtrSENSE4.6 [cache2cache,apps2sd,oc,jit,flash10]-HTC Sense - xda-developers

froyo + sense
[ROM][BETA] TenzoSense - Sense2.2, FROYO, Cache2Cache, OC, Flash10.1, CFSv6 [11-2-10] - xda-developers