What are the 5 culture groups again? Imperial, Chaos, Ork, Eldar and Tau?
Seeing as Necron and Tyranids aren't in yet...
If the Necron and Tau do enter in, I propose:
Imperial- SM, IG, DH, WH- Large impressive buildings, very typically Imperial
Chaos- Ork, CM, LaTD, DE- Generally lots of spikes and dark buildings
Eldar- Eldar- Roundy, eldary, with the wierd Omega shaped... ness
Tyranid- Tyranid- Tentacles. Spores. Goo.
Tau- Tau, Necron- Very square and circular buildings, brownish, lots of glowiness