Ive recently been playing with a program called Dameware mini remote control, basically its a GUI for deploying remote monitoring software accross a network, its similar to VNC infact it probably uses VNC, i know i can connect to any computer using VNC but i need the gui for deplyment for non-technical users!
Dameware is OK, as well as VNC. I'm not aware of OpenSource projects, but there are a few commercial spinoffs with changed layout and reduced user-complexity based on VNC. We use both BestSella and GotoMeeting - the latter a bit more complex but offering bidirectional connections already in the basic version.
We looked at LogMeIn from a software support perspective, and it was not the right product for us. LogMeIn is the right chpice if you want to remote control YOUR OWN workstation. But if you want to troubleshoot a customer's workstation, you can't use it.
The tech-savy customers use VNC directly, the less technical customers get supported wit a GotoMeeting connection, and sales uses BestSella to make remote presentations to a customer.