I find discount direct films are competitively priced with quick delivery.

http://www.discountfilmsdirect.co.uk/

Or Ag-Photographic are good as mentioned in the previous post.

If you are in London. Kingsley Photographic on Tottenham Ct Road are reasonably priced. Although, I recently bought some 35mm Tri-X which cost me 4.99 ouch!!! 120 Tri-X was 3.30 a roll. Ilford film is much cheaper.