I've got a 150 piece set from costco. Its awsome, really good quality and has a lifetime warranty, and was only about £70 I think. (Was a birthday present). I've bought a few bits here and there over the years, from the odd snap on spanner in the most common sizes (13, 15, 17mm), to the cheap type stuff (Draper Expert) that I'm not too fussed about.
A good multi piece set is the best way to start, then just build up as and when you need things imo. Get a big cheap tool box from B&Q or something, so you can just chuck random bits you acquire in it. Simples.
