ReuNet - A Search Registry. 

Reclaiming Your Roots - Support groups and limited registry.

On Line Data Bases - This is a comprehensive lit of many useful data bases.

Yourfamily.com - Support Groups and Registry. Has handy automatic search utility.

Searching For People - Support groups and limited registry.

The Seeker, Reuniting America! - Well organized list of Databases.

Public Records Search - A list of many searchable public records databases. At $30/search, this one could run up a big bill in short order.