Fuzzybabybunny (your name conjures adorable images of kittens and bunnies frolicking in some field, lol, love it)... pretty much nailed it all..
Few other things to add though!
1. Does the flash support high speed sync?
2. Does the flash have any manual controls?
3. Can you do things like flash exposure compensation, etc? How compatible is it really with canon's ettl?
The thing is, canon's flashes imho are worth it. The 430ex II is just about perfect for a rebel. Then if you need more later you can grab a 580ex II and use the 430 wirelessly. The 430 zooms to match your lens (also automatically detects that your camera is a crop sensor camera)... You can control the flash from the camera's menu system...etc. Lots of things that make them worth while imho.
Nothing wrong with some of the cheap flashes though, some of the vivitar automatic ones are favorites! But for on camera use with a canon camera imho the canon flashes are worth it. Nice to be able to just hit the high speed synch button on the flash, or just click the FEL button on the flash, etc...just works.