http://crucial.com/ has both of what you are looking for.
They have some of the best deals on ram around, and they also have a scanner that will tell you what type of ram you need.
If you aren't comfortable using the scanner, you should be able to select your computer manufacturer and model number to see what type of ram your computer takes. They seem to have the info about tons of computer models.
I'd also compare prices with newegg (I've heard they are the best in the US, I wouldn't know, they don't ship to Canada).