"Project-GC is a website aiming to provide dynamic statistics for all geocachers in the world. Besides statistics there are several map tools that might be helpful. For example you can compare your finds with a friend or plot those D/T combinations you are missing. Some of the other things provided are statbars and overviews of your cache series."You can map caches by elevation (no surprise the highest cache in the U.S. is at the top of Mt. Whitney), and calculate your "Caching Karma"; the ratio of cache finds logged on your caches to cache finds that you've logged, or see who has the highest Karma points in any given area. It also has a nice mapping feature that lets you see the caches that both you and your caching buddy have, or haven't, found in any given location; which is perfect for planning your next outing together.
Just one word of warning: if you're a numbers nerd like me, expect to spend hours exploring this site.