Kingston and Crucial (Micron) are the big names, but you'll hear the same from many people here:
Both OWC (macsales.com) and DMS (datamem.com) sell "house-brand" memory made from big-name (reliable, that is) chips that are guaranteed to work with your particular Mac model, and have a lifetime warranty.
I've bought from DMS for years without a problem, and the one time I did get a flaky product from them they immediately mailed me an advanced replacement with prepaid shipping to return the defective product. Both companies have been around for years, so they're going to be around to back up the memory in the future.
In the past I would have said "If you don't mind higher prices and want a guaranteed solid product, buy Crucial direct from them." That's what I put in my G5 tower... but Crucial has some nasty pricing policies--basically, depending on whether you're an existing customer or not, how you shop, and what browser you're using, you'll see different prices on their website. For that reason, even though their products are fine, I no longer recommend buying from them--I refuse to support that sort of thing.
Probably Crucial or perhaps Kingston or maybe NewEgg is the closest thing. Although I'm sure that Canon fans would beg to differ. 