I currently use Streamline and Freedom 2 Surf.
The former is fully featured (FP, PHP, CGI, ASP and so on; limitless bandwidth; good email features) and is pretty cheap. In fact, going any cheaper involves a big loss of features. £47 ex vat for two years on my chosen package.
F2S is not as cheap, and has slightly less functional email; no auto-responders for example, though it does support forwarding. £48 ex vat per year if you include email.
The support of both is quite good; F2S has a slight advantage as it has phone support, but the bang-for-your-buck of Streamline is hard to beat.