I also have had good success with logmein. You might have to look carefully for the free version as they sometimes seem to hide it on their website. Google for "logmein free" should get you there though.
It requires installation on the computer you are controlling, but remote access works through a browser. Great for controlling your pc at home or office when you are out on the road.
It is available for PC or Mac, but not Linux. The remote computer can be Linux based using Java or a developmental plugin - not tried it.
Regards,
Graham