I've been using GotoAssit for a bit, and have been impressed with it's adaptibility and performance. It does exactly what it says it's going to do: it allows remote support for both on-lan and off-lan systems.
The only gripe I have about it is the pricing.. it literally is a product killer. I know that there are other remote helpdesk utilities out there, such as LogMeIn Rescue and mywebexpc, that beat it pretty handidly.