Straight copying .... Nero, DVDDecryptor, CloneCD, etc.
If it's for DVD movie backups though, most commercial disks are dual layer. You will need to compress the contents (or remove contents) to fit it onto a single layer DVD.
DVDshrink is free & does a decent job with the advanced video filters on.
It recompresses large DVD video back to a 4.5GB dvd for you.
Also be aware that many dvd's are copy protected & you may need anydvd to get rid of the copy protections.
Tis interesting that you had problems with nero, although, if you had Easy CD suite installed, it's a no brainer. EZCD causes compatability issues with most burning software.