I just bought one recently for $400 for a mint set with warranty from a nice guy who bought it for backup use but wanted to unload it because he didn't need it anymore. Didn't buy a 580EXII because I was intending to set up a wirless trigger so the master optical trigger capability didn't matter, and I don't really do group shoots so the power and portability of 430EXII was just nice for my portrait use even after diffusing through umbrella.
Put it this way, it was the best $400 I've spent on photography so far. Given the guy behind the camera got what it takes pull it off, I'm starting to see that equipment wise it's always about the light, the glass, THEN the body.
I bought things in this sequence.
450D brand new body with kit lens > 50mm f1.8 > 70-200mm f4L IS > 430EXII
If I could go back in time redo it all over again, I'd do it this way.
450D 2nd hand body (and save the extra cash for good glass earlier) > 50mm f1.8 > 430EXII > etc
I also ordered a umbrella plus lightstand kit from tagotech, a pair of phottix wireless triggers from reddotphoto, and have been having a real blast following the off-camera strobing tutorials and lighting 101 102 techniques from
http://strobist.blogspot.com. Go take a look first and see if strobing is your kind of thing and matches your style of shooting. E.g., you might not need one if you're doing strictly landscapes.
Otherwise, by all means get an external flash (at least a cheap 3rd party one from mass orders section) AND be sure to try out off-camera flash if you want to experience the next level of photography. Actually ANY external flash is way better than not having one because you'll be doing it all manual flash exposure without ETTL or TTL if you are using cheap methods to sync anyway, such as a PC cord or a cheap wireless trigger that is not pocketwizard.
