Synthcube has some good kits and stuff.
Though truthfully, it helps to know a bit about synthesis as well. Start with wrapping your head around subtractive synthesis. Oscillators, filters, AttackDecaySustainRelease. Lots of IC's that condense a lot of functionality into a tiny package.
Personally, I say either get a full fledged semi-modular that's eurorack friendly, build a DIY rack, and start adding to it. Behringer does some GREAT clones of older synths for dirt cheap. I LOVE my Model D.