i use 3 different ones, all used, all dirt-cheap: Yongnuo 560-II,Canon 540EZ and a Sigma 520 (or so). trigger them with Yongnuo YN-622C triggers for canon. those are THE SHIT, if only i could afford (or get myself to affort) a better flash then high speed sync wouldnt be a problem either.
in this case i only used the yongnuo 560 flash, had no time for more.