One thing I have been doing are bicep curls.  I mean, a lot of them.  I start out by doing 20, then 15, 10, and finally 5.  I alternate my arms after each set, and by the end I’ve got nothing left.  Another good idea is to change it up a bit if you start to plateau.  Come up with some different set ideas, or alternate the reps.  20, 10, 5, 15.