One of my personal favorites is RemoteDesktopManager (http://remotedesktopmanager.com). I use it extensively for working with client machines on a regular basis, as well as controlling the VMs at our CoLo. It supports all of the popular connection methods, and has an extensive plug-in seleection. If you're willing to pay a modest fee, it can be used in enterprise mode and its resources can be shared throughout your network. It also supports access and security at the user level.

A great tool for those who do a lot of remoting!