I've been buying quite a few strategy guides lately. I've probably bought around 30 guides in the last 3 months. I managed to find some older ones on ebay for cheap, but shipping is a killer.
EBGames recently started carrying guides again but they only get about 3-5 copies of a guide for a big name releases (Fallout, Fable, Gears 2, etc). They give you 20% off the guide if you bought the game there.
Most of my guides I've been buying from Chapters.ca. They don't stock them in-store, but they have pretty much everything I was looking for and they are always 20-25% off, usually beating EB's price even with the 20% off. If you are spending over $39 the shipping is free. Amazon.ca is pretty much the same deal as Chapters.ca, they are pretty equal for prices and the free shipping deal.
My problem is what to do with the guides when done. Shipping in Canada is too much to ship them anywhere to the states; not sure about shipping within Canada but it's probably not any better.