I've been wanting to purchase one for a while, the other day I decided to do a search to see what they cost and came across this app for my IPhone, needless to say I purchased the military version right away. Have not had a chance to use it, but it will make life much easier that doing manual calculations that I used to do.

here's a link to the one I got;
http://www.knightarmco.com/bulletflight/index.htm

Figured I'd start a thread on them and if others have used different brands and their thoughts.