What type of flash photography are you desiring to shoot?
If you just want a good flash to use on the hot shoe then I'd say get the AF540 and you're set.
If you're wanting to start doing off-camera flash work then there are a bizillion different directions to go. I (so far) have the AF540FGZ, 2 Vivitar 285HVs, an AF280T and an AlienBees AB800 monolight; and a metric ton of supporting gear to go with them all.
If you're just getting started with "studio" style flash work though, the 360 is all you
need right now. Take yourself and that flash over to
Strobist: Lighting 101