Although I'm not a geek... well... maybe I'm am little geeky. I give you:
The Degree Confluence Project which seeks to visit every integer latitude and longitude degree intersection on earth and photograph each location. I need a digital camera and a GPS receiver. Unfortunately, it looks like most of the civilized world has been done already. Good thing I live in Los Angeles. (Via Mutated Monkeys, who inspired this post.)
The Wooden Periodic Table of the Elements which is an actual table with receptacles for collecting every (known) element. The creator has samples of every element with a half-life of greater than 1 year. Yes, I'm jealous.
Geocaching, the sport where YOU are the search engine. People hide stuff at GPS locations and then post the coordinates to the site, allowing you to go find them. Yet another reason to get a GPS receiver.
Action Squad, the website of a Minneapolis-based urban adventure team. They sneak around old buildings, caves, mental hospitals, &c., and photograph their missions. It reminds me of my undergraduate excursions through the steam tunnels under UCLA. Hey Matt, do you still have the map we made of the tunnels?