Well, maybe it's my age or perhaps the fact that I REALLY want to ward off high blood pressure and all those other ailments that come with age, but now I'm a big fan of running.  On days that I do not run, I feel like I didn't accomplish enough for the day.  

These sites below have helped to motivate me and increased my drive to get healthy.  I've tried a few others, but these rose to the top.

MapMyRun.com - Map your Runs, Running Routes. Calculate Calories, Distance, and More.

From their site:
MapMyRun.com is a community web site for runners and joggers who want to stay healthy, lose weight or train more effectively. MapMyRun.com provides easy-to-use, comprehensive web-based running tools, social networking, running iPhone applications, and running maps to measure distance and count calories from running.  With running forums, training logs and tips from expert runners and coaches, MapMyRun.com is the social network where runners are.

From Damon:
Blah blah blah.  The "social network" claim is weak - I don't think that many people would be keen on meeting some random through this site.  However, their Google Map tracking tool, training calendar and awesome price (free) make this a great site.  It has motivated me.

Hal Higdon's MARATHON TRAINING GUIDE

This site seems to be the definitive source for those crazy enough to attempt a marathon.  My aspirations are a bit lower, but staying on track has been a great experience.

One Hundred Push Ups

From their site:
The hundred push ups training program designed to improve strength and physical fitness.

From Damon:
It's not running, but It's cool to say you can do 100 push ups.  So, here I go.  I'm on week 3 right now.