I can second logmein and the paid for pro version is even better. I use the pro version to support my dad and his home network in Brisbane from here in the UK. Its quite a big home network too..what with 2 adults and 4 Uni aged teenagers! I'll let you guess as to the amount of networked kit! Seems like I'm on Dad's network every few days sorting things out....!
It's also good for letting me pick things up from my own PC when at work or travelling away from home. I quickly found out how useful that can be.
If you admin a network of anymore then 10 PC's then it's no contest
Netsupport Manager has to be the winner.