Remote Desktop Connection for Mac OS X
If you want to connect to a Windows machine (XP Professional or any of the “Server” products), you can actually use Microsoft’s own remote desktop connection.
OS X only, but great if you don’t want to clutter your machine with Office, etc. – just use your local network to have a window open to your Windows box.
Lloyd originally pointed this out to me, and they had pulled the download at some point, but it’s up now.