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Can anyone recomend a cheap place to get 58mm filters on-line? Need a UV and circular polarizer. 7dayshop were doing a set of 3 for £18 but they no longer have stock and can't say when they are getting more. :evil:
The cheapest place I know of for quality filters is Dixons actually. They stock Hoya filters at prices that most other places don't come close too. The problem you may have is finding a Dixons branch with the ones you need in stock although you can order online if you want to.

Failing that try SRB as they stock filters for most size and fits including Cokin filter systems and Lee filters. They also make custom filters at reasonable prices and are very quick at delivering. I have used them several times and found their service to be excellent.

SRB link
Jessops do their own brand. Not sure of teh quality, as I've never used them, but they're cheap. Basiclaly however, your lens is only as good as the worst piece of glass in it, or indeed on it. For that reason I rarely even use a skylight or UV filter. When I do use a filter, it's a B+W or nothing.