Here is an excellent exercise from the Russian piano tradition passed down to me from Vladimir Feltsman. It works on our weakest finger, the 4th, without straining the hand. A symmetrical finger workout is the best kind, in my opinion. And when you continue through all 12 chords chromatically, this takes your hands through a variety of black/white key landscape and teaches wrist flexibility as well.
Please DO NOT ever practice this exercise at a faster speed than indicated on the score or you could injure yourself. Slower is fine.