looking for an flash that's a good optical slave...

I've been looking for a few off camera flashes and thought I would just get RF triggers for each flash and get a few of the Yongnuo 565's when they come out, or some other cheap flash. But then I read where I could just get 1 set of RF triggers, and use the others as optical slaves. So I'd like some advice!

I'm not sure which would be best, but I think my options are these:
- Get extra radio triggers with any slave
- Get external optical adapters with any slave
- Get opinions on cheap flashes with good optical sensors

I'll also add that I would prefer semi-powerful flashes like 430EX equivalent or more. Any opinions?

I'm not a big fan of relying on (simple) optical slaves. They are fine in a studio, or a small room, but I've had too many issues using them outdoors, or at events where other people who are popping off a flash to be a big fan. Using a receiver for each flash is the best option. If you decide you want to try the optical slave route I think most of the YN flashes have built in optical slaves with two modes, one that ignores the preflash from ettl flashes.