Online Ballistics Calculator

[1.618]

Best one I've seen online:

http://appliedballisticsllc.com/ballistics/

I've read Bryan Litz's book "Applied Ballistics for Long-Range Shooting" and he really seems to know his stuff. Highly recommended.

[mikein]

Here's a pretty neat one, and you can carry around with you on your iPhone or iPad:

https://itunes.apple.com/us/app/istrelok/id319662395?mt=8