two additions (to a useful list):
1. SQuirreL - a true multi platform SQL Client. Supports SQL Server, Oracle, Access, MySQL, Firebird, PostgreSQL, Sybase,Informix, Excel, text files, and more....from ONE interface. It's not the ideal tool, but it is good, easy to use, great (free) support and if you're working with different databases, there is nothing else around that I know of...
http://squirrel-sql.sourceforge.net
2. Forget Yahoo - though an improvement over MSN, it's a million miles away from GMail (which includes integrated chat window)