One of the finests aid to pbem is the Automated Card Tracking System
, developed by Kurt Kuhlmann as a web application to support the Avalon Hill's Card Driven Game We the People at the end of last century. It has been expanded during this time, slowly but continuosly, and now it has 24 differents modules, one of them is a generic module that allows you use this service with virtually any board game.
You must only register (at the beggining you registeres sending an email but now there is a form available to submit your data) to begin to use this aid. Be careful to provide a valid email because this application does a high use of email services.
I guess the high popularity of this game aid is owed to sending an email for each action realized (send message, roll dice, and so on) to each player registered in the game. Also, his game journal, where is logged every action executed under the module, is very useful, allowing revise the complete log from the start of the game.
Unhappily, during last year it was hacked several times with the loss of users and cards names (I don't know who can be interested on it) but it seems that security has been improved. Last feature added is Custom Module, where you can now design new modules for those games not available. Now that I'm revisiting Cold War from Victory Games, I will go to make my first custom module design using this option.