I have some issues as well with SLI. When I disable SLI it does not happen as often, but when I have it enabled there is a 70% chance that I will not survive a 30 minute video withouth BSOD. However, I do not have this problem with video games.
Another tip to check is your temp, mainly GPU. Install speedfan and keep an eye on the temp levels. My 8800 GT since they are single slot get quite hot sometimes.