Any good amp/pre-amp kits out there?

Has anyone ever tried building their own amp or pre-amp? Are there any good kits available? I'm looking for something around 20 watts.
Audio Note
A friend runs a "whole deal" Bottlehead Foreplay preamp, into an NAD amp,into a pair of Madisound Cygnets.

In that system,the Foreplay does a fine job and is fairly priced.
Thanks for the replies. I should have said I am looking for solid state - that sounds as good as tubes :-).