Depends on what you intend to do with it. Obviously, there is a lot of decent "generic" memory out there, and a lot of not so decent stuff, too. With prices being so low, it doesn't seem worthwhile to save a few bucks on a questionable purchase. That doesn't mean you need to go all out, either. A few things to keep in mind:
1. Athlon/Duron/T-Bird systems can be picky about ram, call the vendor before you buy any ram not specifically rated for these systems.
2. Even "budget"ram from quality vendors will perform as advertised; if you push it, the stuff will likely fall on its face.
3. A lifetime guarantee is only good for the life of the company, stick with vendors who are likely to be around for awhile.
4. Check out the hot deals section here and other forums, there are quite a few out there right now....