I have the exact same problem -- while doing my deadlifts on box (95 lbs), I had to stop midway in the second set and put on lighter plates because I would have dropped it otherwise. I have decided training my grip strength is probably a good investment, since it is correlated with health and upper body strength.
This is a pretty good starting article on the different types of grip strength and how to improve it.
And Mandos, thats a great suggestion
