In my experience, ensure that your amp is at least 100W/channel. I made a foolish mistake and bought a Pioneer 80W amp last year, and it just does not cut it.
Also - Unless you are a complete Audio Freak LOL you can pick up a decent 5.1 amp for about 250-300 CAD. JVC, Pioneer, Kenwood are pretty much identical in quality, but JVC likes to penetrate the market...so you could get alot more for your money with JVC.
Spend as much as you can on the speakers - they are the most important part IMHO
JBL and Polk make GREAT speakers for very little money.