.NSF (Nes Sound Format) is the NES's music format. .NSFs can be ripped from games or created in Famitracker. They can be played in quests via Enhanced Music or in winAMP using the chipAMP plug-in. They're a great fit for 8-bit quests so use them if you can! Here are some great .NSF resources to get you started:

Music rips of all known NES games:
http://www.zophar.net/music/nsf.html

Lots of great Famitracker artists. ASK ARTISTS FOR PERMISSION!!!
http://famitracker.com/forum

More music created by various artists:
http://2a03.free.fr/?p=pub&type=nsf

Shovel Knight soundtrack:
http://virt.bandcamp.com/album/shovel-knight-original-soundtrack

