Expedia's Mileage Manager
As you know, I don't really cover frequent flier programs here on CompareRewards (something I may address sometime in the not-so-distant future, however).
If you are into those points programs, you may find this tool from Expedia helpful -- it's called MileageManager and is free for the first 30 days, and $4.95 annually afterward.
Not only does it track your program balances, it keeps you updated on current bonus opportunities, mile expiration, and more.
You may also want to consider USA Today's MileTracker program, which is free.

Date: June 21, 2007 12:06 PM
Another free program that can track your miles (as well as credit card and bank balances) is the online Yodlee. A demo is at http://corporate.yodlee.com/moneycenter/PFM_demo.htm
registration at
https://moneycenter.yodlee.com/moneycenter/registration.moneycenter.do?_flowId=registration&c=csit_key%3Ah8rKgtr0SlsX90Sp%2FaOKDZsE9Bw%3D&l=_flowId:u
Scott
Date: March 13, 2008 1:22 PM
You can also try http://www.AwardWallet.com.
They have web and mobile access. There are both free and paid options.
There is a flash demo of the site at...
http://www.awardwallet.com./screencast/
Date: June 24, 2008 6:01 PM
You can also check www.pageonce.com - web 2.0 solution to track awards.
Date: July 16, 2008 9:54 AM
The same MileageManager that Expedia offers for a fee is offered by Forbes Traveler for free, http://www.mileagemanager.com/forbes.php .