I used WMM at first which is great and easy, but you lose so much quality that when I switched to HD cams it makes a huge difference (even the Windows 7 HD version of WMM).
So I tried a few free ones and looked at reviews and eventually 'bought'
*ahem* 
Corel VideoStudio Pro X3.
Quality is great, and for simple editing (add an intro, cut footage, create in chosen format) it's straight forward, with loads of extras I'll never use and some useful stuff like fades that I do.
It can get a bit complicated and was a bit of a bugger to work at first - but that's probably more down to a Monkey In Charge error.
The only problem I find is when you're actually editing the footage it plays very jerkily so that bit isn't ideal, but it's still useable. It makes it a right mission to overlay text on the right bit of footage, though - like in this vid:
[youtube]http://www.youtube.com/watch?v=ei43fI7Y7kc[/youtube]
I never realised just how much of a minefield it is out there until I decided to upgrade. You could spend a hell of a lot of money and get software that's pretty much useless! I'll be sticking with Corel for a while, because it's plusses far outweigh the niggly things, so far.