$100-150 US or Canadian?
These questions always result in some varying answers. Some will tell you to buy a 580EX Speedlite (the high end of the Canon line), because it's not their money. But very few amateurs will ever use all of its capabilities.
The 430EX is a great flash also, and quite a bit cheaper. It's the lowest priced Canon Speedlite that can rotate up for bouncing and also swivel sideways. There are cheaper Speedlites, but if you buy one that doesn't swivel, you'll eventually wish you had one that did.
The Sigma EF-500 DG ST goes for about $150 US. It's powerful and has bounce/swivel capability. It lacks some bells and whistles of the higher priced units, but it will handle 99% of what most amateurs use a flash for.
Before you buy, it might be a good idea to read The EOS Flash Bible (link in my signature) to familiarize yourself with the terminology so you can make an informed decision.