What flash to buy?

So I want to get flash for my 20d and can't decide which route to go. Really would like to keep the initial purchase under $500. I know that on camera flash sucks for almost everything, so I am tempted to go the strobist route and just buy a nikon sb24 or vivitar 285 and PWs or crappy imitations.

But, then I feel like it might be nice to have a flash that I can use in my hotshoe with ettl or with a canon off camera shoe cord. That leads me to a 430ex or 580exII. Is the 430 just incapable of bouncing in a realistically sized room? Is the build quality on the 430 okay? Also, I have heard the the mk II of the 580 isn't worth the extra money (Underexposure issues, crippled pc sync when using as a master, etc). Verdict on the 580exII?

I realize that no option will do everything I want, but where should I put my money to at least start building a lighting kit?

In order of priority I see myself using this flash:
1. Screwing around with strobist type things
2. Fill flash for around the house
3. Maybe for some off camera sports shooting (dirt jumping, maybe climbing) but I realize this is probably not that realistic without multiple off camera flashes