My ipod has so many odd songs on it, including Mary Had a Little Lamb (by Stevie Ray Vaughn), the Polish National Anthem (performed by Happy Louie), several midi versions of popular songs (Knight Rider Theme, Macgyver Theme, What is Love), the music from Sim City 3000, some hilarious songs from edible castle (No Forks), even some of the songs from the Brave Little Toaster and sequels (Cutting Edge, B-Movie, Home Again). I'm pretty wierd like that.
However, there are some "good" songs on it as well, that weren't very popular. The Big Generator CD by Yes had some great songs, like I'm Running (A song with a strange rhythm and two different musical themes, one happy and one mysterious), Almost Like Love, (I find this song funny, but it's a good song) Shoot High Aim Low, Holy Lamb (both slower but very powerful), and of course Big Generator (So random and exciting, and some cool horn parts).
Some good songs by Asia as well, like Time Again (my favorite on the particular CD), Cutting it Fine, Sole Survivor, and Without You (They're all kind of pop, but still have some rock in them).
Days of the New have some pretty good songs too. The ones I find best in a way that others will probably like it are Skeleton Key (Just music that reminds me immensely of Crash Bandicoot), Shelf in the Room, Enemy, Bring Yourself, etc.
Finally, Subdivisions and Working Man are great songs by Rush, but I'm not sure if those are actually unknown songs. Probably not, but worth listening to if you haven't heard them already.
Sorry for the long post. I have a lot of songs that I really wish other people knew about.