I've been starting to use Vallejo colours more on my models, you can pick them up pretty cheaply at Wargames and Figure shows (I think the last 4 pots cost me about £2 each) and the two ranges, Model Color and Game Color provide a fairly extensive range of colours. Consistency-wise, they tend to be a bit thinner than GW paints, but that's by no means a bad thing.
I'm sure others have more experience with them though. Just my two cents.