Underestimated, song, artist or group '' gems'' ?

I'd echo Synthfreak's recommendation of Nick Drake. Especially 'Pink Moon'. Timeless (even though it's over 30 years old).

Also;

XTC- Nonsuch
Peter Gabriel - Passion
Budd/Eno - The Pearl
Michael Brook - Cobalt Blue
Talk Talk - Colour of Spring
Lou Reed - Magic & Loss
Miles Davis - In A Silent Way

Additionally, the ECM catalog is littered with gems.

CD

Burton Garr - Mighty Long Road
This is the blues artist the record stores in the Big Easy listen to. Find it, buy several copies and share with friends. Easliy the best find I've made in 5 years.

I second the Richard Thompson nomination. Although he has even been nominated for a Grammy or two, the average music fan has never heard of him.

I'll also nominate John Cale. He's been consistently over-shadowed by Lou Reed in terms of both popular and critical appeal, but for my money his post-Velvet work has been much stronger than Reed's.

And how about Graham Parker? The forgotten member of a remarkable late 70's new-wave triumvirate (along with Elvis Costello and Joe Jackson), his body of work is arguably the best of the three (although admittedly less adventurous). Yet he has no profile at all in the States, and most of his albums are out of print.

Three pop/r&b nominations:

NRBQ - Yes, they have their devoted grassroots legion, but it's criminal that they never got much mainstream attention. I don't remember EVER hearing an NRBQ song on broadcast radio. And they have to be one of the hardest working bands on the planet.

Francis Dunnery - Apparently had more of a following in the UK from "It Bites" - but he's a bloody great guitarist (touring back-up for Robert Plant and Santana among others), and his solo career essentially went nowhere. You'll hear "My Own Reality" and "Too Much Saturn" on radio occasionally, but all of his albums that I have (Fearless, Tall Blonde Helicopter, and Let's Go Do What Happens) are definitely keepers.

The Pooh Sticks - Deserved to be huge (but weren't).

I appreciate TWL' s mention of Urge for Going, which was just about first song I learned to play on guitar back in 1968. I was playing Tom Rush's arrangement. He was an inspired scout of great songwriting talent (Joni, Jackson Browne, James Taylor) and not a bad interpreter of the songs, either.