As far as editing goes, and I know this has been mentioned before, I say these three are the best, in this order:
- Avid Xpress DV v3.5 - $1,699.00
- Final Cut Pro 3 - $999.0
- Premiere v6.5 - $549.00
As for actualy DVD authoring, I'd have to say
DVD Studio Pro ($999.95) on the Mac, and (for the very serious)
Scenarist ($2995.00 - $7999.95) on the PC.
Keep in mind, this is assuming you have a budget for the software, are completely dedicated to creating a quality product. I wouldn't say these are for people just fooling around, unless, of course, you just happen to have a ton of money to throw around, then why not.
I tend to always want the best of the best, hence the reason I ended up with an Empeg.

I'm sure a lot of others think the same way.