I can only recommend what I know...

Tartans:
BearKilts
USAKilts
CanadaKilts
(to a lesser extent) StillwaterKilts

Solids
PittsburghKilts
UtiliKilts
FreedomKilts
AmeriKilts

Traditionals:
BE CAREFUL... 8-yards does NOT a "traditional" make!
In the USA, give KathysKilts a yap
In Canada, try Hector Russell
For Europe... read any post from Hamish!