Ben Harper's "Diamonds on the Inside" is a wonderful song that never gets the recognitiion it deserves.
"Save it for a Rainy day" by the Jayhawks and "Car Wheels on a Gravel Road" by Lucinda Williams are both wonderful pieces that many people haven't heard. I could fill a whole page with Wilco songs that deserve to be heard.
I'm a huge Replacements fan and most of their really good stuff never got much play. "Achin' to be" is a perfect example. It's such a soulful song.
For truly excellent "fun" music a band out of Georgia called Marvelous 3 is absoultely amazing. They never got the recognition that they deserved. My name comes from one of their songs