One of the members of the Folding@home team, Imran Haque, has developed a memory tester for GPUs. You can get a copy of it here:
and here's a brief description:
MemtestG80 is a software-based tester to test for "soft errors" in GPU memory or logic for NVIDIA CUDA-enabled GPUs. It uses a variety of proven test patterns (some custom and some based on Memtest86) to verify the correct operation of GPU memory and logic. It is a useful tool to ensure that given GPUs do not produce "silent errors" which may corrupt the results of a computation without triggering an overt error.
Basically, the idea is that we wanted to put out a code to test GPU memory that's roughly equivalent to Memtest on CPUs. If you run FAH heavily on a GPU, it's a good idea to check out your GPU memory, just as one would run tests on CPU memory.
For now, this is being hosted on Simtk.org, the scientific software repository at Stanford, but we will likely move a copy to the FAH download page in time. If you're having any problems with the GPU MemtestG80 software, you can leave a bug report on the Simtk.org page.