I'm going to throw my hat in for GeoBallistics. Pretty comprehensive bullet library and has a built-in mapping feature to measure out distances and mark multiple targets. They make a wind meter ($40 & $80 depending on features you want) that has been very accurate for me.
I like Geoballistics (ballisticsARC) as well. It uses the same jbm library many do so the results will be the same but also allows you to also use satellite info for finding ranges and building range cards.