I'll add Mather's of Lancashire, 7dayshop, Mailshots and if it is Fuji film then Fujilab and Digitaltruth who sell the Legacy 100 and 400 which I am told is in fact Acros and Neopan 400 respectively.

No one site wins the accolade for being the "best" source on film but AGphotographic comes very close. It stocks a great range of film and sells lots of other analogue stuff.

Have a look around these sites and then decide