I found DocMemory about a year ago and it is a great piece of freeware. If you ever are firing up a new system with unproven RAM and you want to see how high it can overclock this is a good way to find out how high it won't go. Since it runs of a floppy you can test your RAM without putting you hard drive at risk. The bad thing is that the speeds you can run your RAM error-free in DOS mode will probably be higher than what you'll get away with in Windows. Be careful.
Of course, if you have a friend with computer problems and you suspect one of his two memory modules are toast, this'll prove it.