As a general rule of thumb, I always consider RAM as the most likely culprit.
But it could be something software related, though less likely imo. Create a new user and log in as that user for a bit and see if the problem disappears, if it does, you've got something going on with your user that OSX doesn't like.
How hot is the system getting? If you leave it turned off for a day, can it stay on again for a while, vs. rebooting and having it crash again quickly? I know I have a dust buildup issue with three cats in the apartment.
Compressed air can probably blast some dust out. I'm not sure how easy it would be to open the case and blow it out.
It's a good thing I thought about computer temps. I checked mine and saw the video card was at 73C . Turns out the fan on it died. Here's my temporary fix: