I've been using ukonline for the pass 6 months and have downloaded quite a lot (as I had to reformat my hard disk and didnt save any personal files!)
They've been quite good and so far, there is no download or time limit, the price at the moment is resonable too.
If you go for an ISP, go for one which offers an umlimited download rather than one which limits your download to say 2GB per month.