The best thing that I've seen is DVD-Lab
from Media Chance. It's not free, but for DVD authoring, it's VERY
cheap. It also beats the heck out of most other tools that are anywhere near it's price range. You can easily go out and spend 3x or more (much more) on a DVD authoring tool and still not get anywhere near the same quality.
One of the major problems is that many DVD authoring tools encode the material for you, even if you've already got the right AC3 & MPEG-2 files. That just leads to quality degradation, which is just stupid. DVD-Lab follows a more professional approach and gives you more control. It's not for total beginners but it is easy to use.
The menu authoring in DVD-Lab is top notch as well.
Just so that you know... A professional level DVD authoring tool will run you $25,000 at the low end. (Or at least the last time I checked - they may have some down a bit - not too sure.)
If you're just looking to make some boogery "My Family Vacation" DVD, then DVD-Lab is overkill. But if you want to present things in a more professional manner, you can't go wrong with it.
Last time I used it (a while ago), it was a bit particular about things and really wanted proper files - but that may be fixed and you may be able to use MPEG-1 video (which you shouldn't be able to do...).
Anyways... Just throwing that out there for you.