Have you looked at memtester? What do you think of it?

I've successfully used memtester in the past to detect suspend-resume memory corruption on my desktop, just by periodically suspending and resuming the PC while memtester was running. It helped me to confirm that that particular desktop really has some memory corruption issues (while other PCs I tested on didn't). So in this particular case I was satisfied with the tool.

The downside is that it's a userspace utility, so it can't test the whole memory. When I e.g. purchase a new RAM stick, I prefer to boot into memtest86+ (I switch to BIOS mode to be able to boot it) and test the whole stick with it. Anything running inside an OS can't provide you with the same level of verification.