VNC
Pros:
Works with Vista,
Requires no installed client software (the client they give you doesn't need installation, and if thats a problem, you can use a java enabled browser to connect to the server).
Free,
Does not require you to send data to any other server apart from the machine you are connecting to.
Generally quite efficient.
Cons:
Can be a bit slow on some kinds of video.
Does not carry the sound over from the server.