dont forget the 420 ex which was the previous model - that cant be got new anymore but its often available
second hand and is still a damn good flash - also its worth keeping an eye out for bargains on the 580ex which is the big brother and a lot more versatile (but hence more expensive unless you get lucky).
Or as jeremy says take a look at a reputable third party brand like metz or sunpak - the only downside to these is they are as , if not more, expensive as the canon kit
(one other note re buying
second hand , any canon flash which ends in EX will be fine , but dont be tempted by 'bargain' prices on ones ending EZ these were the previous itteration and dont work propperly with the digital SLRs - though they can still be used with remote triggers or slave units as second or third off camera guns)