One of the software tools I used to rely on every single day was Windows Live Mesh, because it could synchronise large collections of files and provide remote computer access in a simple, set-and-forget way. Microsoft decided to can that entire useful service to focus on making a Dropbox clone instead, which is what led me to install TeamViewer on all my computers. My cousin-in-law pointed me to it, and I can't thank him enough.
TeamViewer does the remote access job of Live Mesh, plus a couple of other tasks, and I am very pleased with it. It works faster than Live Mesh did, and more reliably, in my experience. Once I'm logged in on all my machines, I just choose one from a list, double-click, and it's like I'm right there in front of it.
But TeamViewer has a few extra tricks up its sleeve, too. You can start a one-to-one VPN with a connected machine, too, which allows you to transfer files and access private web services too. That's pretty handy. And with the Android app, I can do all this from my phone as well.
The most useful thing it does, however, is allow me to connect to family PCs for that all-too-frequent family tech support. I set it up on my Dad's machine, and if he's having trouble, I can log in and help, rather than trying to talk him through it blind, which is like helping a panicky passenger through land a plane over the radio. It's much better to actually see what's going on and be able to help with my mouse and keyboard.
For all these reasons, TeamViewer gets my personal recommendation, and it's staying in my toolbox.
Mokalus of Borg
PS - It's free for non-commercial use.
PPS - I haven't needed it for commercial use yet.