My favorites are Gymboree, Petit Bateau, Janie & Jack and Zutano. A lot of people like Hanna Andersson also, but I haven't ever found anything there. Also, Naartje is supposed to be good. Buying cute baby clothes is so fun!!
ETA--The Gap has some pretty cute stuff too actually (sometimes cuter than their adult's clothes, IMO. Ralph Lauren's baby line is also sweet and they hold up well.