there is already a pop-up flash in 500D...
if you want to consider external flash, and to stay within your budget, try B&S section bah.
580Ex would be a good buy, but i am sure sure if you can get it within budget
What makes you thinking about external flash? What do you hope to achieve? For which purposes do you needed it? Or are you just trying to 'complete' a setup cause other people also have an external flash?