I'm also looking for something better to support my clients online. RDP is great, but it does take a few minutes and allot of patience for the average PC user to setup over the phone. Logmein is great, but only for established clients where you have the chance to setup the client correctly... physical access is best.
VNC is ok, but performance and stability is an issue. Crossloop would be ok, but your advertising their service, more so than your own.
RDP is the way to go.... just have to perfect a system for configuring the target machine, maybe a batch script to create RDP user, turn on RDP, forward port on the router (PNP), and piing back a certain IP to announce availability.
Shouldn't be that hard, right?