20gb! you'r elooking at 3 DL discs or about 5 SL discs.
for DL do not go for anything other than verbatim...especially if you want the data to be accessible in the future!
for SL, i'd go with verbatim or taiyo yuden. there's a sale right now on sonys at best buy. if you can find spindles that are made in japan those are top quality media (made by taiyo yuden) and are a very good choice
i'm nto sure if your burner supports booktyping (bitsetting) if it does, i'd go with a +R media booktyped to DVD-ROM. if your burner does not support it then -R would be most compatible with the widest array of standalones. (I'd test out how your burner reacts to -R DL first though since it's newer...many burners do not yet hae adequate firmware support for it.
make sure your firmware is up to date and you should be goo dto go.