I find practising scales exercise the pinky quite a lot (with the "correct" fingering). Plain old major scale up and down will do fine, but also try e.g. 1-3-5-2-4-6... (The numbers refer to scale degrees, so for an A major scale it would be A-C#-E-B-D-F#...) If you e.g. start with your middle finger on the lower E string, 5th fret A, the pinky will be used on the E and the B and so forth. This can of course be varied infinitely with different scales and patterns.
Another thing to try are power chords with an added 9th:
%1/1.3/2.5/4.0/0.0/0.0/0
I think they sound pretty neat and are fun to play around with, something which is hard to say about scale exercises.