Is there a good DVD burning/backup software that is free?

What operating system?

For Macs, I'm in love with disco, which is not free, but is cheap-- http://www.discoapp.com/

How about for Windows?

I really like CD Burner XP pro. You can find it on www.download.com. Look under "Audio & Video" then "CD & DVD" burners. Totally free. I use it a lot, no problems. The CNET editors seem to like it too. I use it for backups, burning iso images, lots of stuff.

Oh, not nag screens or anything annoying either.

If you're looking for a more mainstream program, Nero Burning ROM is pretty fantastic. It's attainable illegally for free, though it's also not all that expensive, comparatively. I like the newer versions a lot, and it'll do pretty much absolutely anything. The only thing it won't do, really, is rip copies of copyrighted DVDs.. but not a lot of regular burning software will. For that you'd need a different program, most of which you can get for around 30 bucks, or, again, illegally - like most things on the internet.

I second Nero Burning ROM -- the 2nd best thing to buying a Mac =)

Also for converting DVD’s take a look at VLC.

Also, I believe handbrake has been released for windows
http://handbrake.fr/

But VLC is it for me!!

The nest website for finding free software is techsupportalert.com It is updated all the time and the authors of the site rank the software for you, giving you the pros and cons of each. They only deal with free software and are normally up to date with newer software. Also the forums at the site are always active