If I'm in a hurry, certainly the local camera shops (here in Denver, there is only Englewood Camera and Mike's Camera). They carry the basics (just Kodak, Ilford, and Fuji) and at about a $1-2 more per roll than B&H. Not too bad for the convenience IMO.
When I was in LA, Freestyle was the place. But their shipping cost sends me to B&H now if I'm ordering online.
+1 on Fotoimpex.de. They have Rollei films (including bulk) for 30-50% less than B&H and their shipping was fast to the USA.