Open water: Just about any small jig under a float at the right depth when the water is cold, the same jig tossed on light line when the water warms. My favorites are 1 1/2" tubes on 1/64 oz. tube in white, chartreuse, gold or silver glitter, or any combination of those colors. Also good are 1" twister tails in pumpkinseed, chartreuse, or white on 1/64 ounce jigheads. Power wigglers on 1/80 oz. jigheads are awesome as well. Ice jigs tipped with maggots are also very good under a float.
The key to catching crappie is finding them and what depth that they are at. Vertical jigging for them is effective to if you can stay over the school.