The short answer to your question is that Macs with SuperDrives are designed to support DVD-R exclusively (but that may be changing). If you buy these, you can't go wrong.
There are other competing standards, here's a summary, courtesy of
dvdrhelp.com
DVD-R and DVD-RW
DVD-R/W was the first DVD recording format released that was compatible with standalone DVD Players.
DVD-R is a non-rewriteable format and it is compatible with about 91% of all DVD Players and most DVD-ROMs.
DVD-RW is a rewriteable format and it is compatible with about 74% of all DVD Players and most DVD-ROMs.
DVD-R/W supports single side 4.7 GB *DVDs(called DVD-5 ) and double side 9.4 GB *DVDs(called DVD-10 ).
DVD+R and DVD+RW
DVD+R/W has some better features than DVD-R/W such as lossless linking and both CAV and CLV writing.
DVD+R is a non-rewritable format and it is compatible with about 86% of all DVD Players and most DVD-ROMs.
DVD+RW is a rewritable format and is compatible with about 74% of all DVD Players and most DVD-ROMs.
DVD+R/W supports single side 4.7 GB *DVDs(called DVD-5 ) and double side 9.4 GB *DVDs(called DVD-10 ).
[ October 10, 2003, 09:11 PM: Message edited by: PGant ]