The claybar that someone else suggested would work, but is very time consuming, and expensive to use on a regular basis. Not only that, but you must be very careful when using it, if an abrasive (like dirt) gets caught in the clay, you risk rubbing scratches into your paint. Used correctly though, it's perfectly safe.

I have to deal with tree sap constantly on my cars, and I use Eimann Fabrik Power Wash +. It's cheap, and strong, yet will not strip your wax. The problem is that it's mail order. But it will deal with sap, I know from experience. Here's a link...

http://www.properautocare.com/pw-32.html

KC