Steve Blaze of Lillian Axe. Great lead and rhythm guitarist and great songwriter. He was in Guitar Player's Top 100 Underrated Guitarist a while back, I think 2007. I can't find the article but I think he was number 47.
Lucinda's groups are always world class.....have seen them all, and they never fail to entertain...love them.
Johnny A. Not as much "underrated" as much as "unrecognized" . . . but I love his tone and his taste is impeccable. Watch the guy do "Wichita Lineman" and "The Night Before" (Johnny A. - "The Night Before" / The Beatles »). Not flashy, but very melodic and creative. He is currently on the road playing lead in the new "Yardbirds".
I saw Neil Finn listed here on someone's long list of favorites, but I'd like to single him out because he's really well known and beloved as a fabulous, melodic songwriter, but I've recently been on a Finn-related listening jag and I've begun to pay attention to the fact that Neil was drafted into Split Endz as their new lead guitarist at age 19 having never really played lead guitar or even electric guitar very often (he began piano at an early age and is an amazing pianist, as well) and he quickly became a very profeicient lead guitarist for Split Endz. Then, when he started Crowded House, they were just a three piece (by the time they recorded their first album) and Neil's guitar playing is astonishing on those CH albums and live, as well. He's so incredibly versatile and his ability to play riffs and various complex parts, filling out the live sound all by himself while also singing the songs is remarkable. He's truly one of the most gifted all-around musicians alive - as a singer, guitarist, pianist and even drummer. I think maybe only Paul McCartney can rival him,
Better yet, the venue was on the second floor of Irish themed bar (northern Kentucky), and about thirty people. Intimate, comfortable, good acoustics, sat directly in front, talked and got autograph after the show. Great experience.
The greatest guitarist I've ever heard or seen is Chris Risola of Steelheart, but I can't blame anyone for underrating him because...Steelheart. Who wants to listen to that. But those guys are from my area, I took lessons from Chris when I was a kid, and I saw him play live many times before SH were signed, and heard him play many different styles. And he's the best. No question.
Martin Barre/Jethro Tull: His style and tone are as personal as a fingerprint Glenn Tilbrook/Squeeze: Great melodic and fluent soloing on songs like "Another Nail In My Heart" and "Black Coffee In Bed" Keith Urban: Contemporary country is NOT my thing, but this guy is a real "player" Michael Sweet/Stryper: For those in the "know" this is not news. But he oftentimes carries the stigma of a rhythm guitar player when he is part of a twin guitar attack and possess great technique
Two more great picks. I'm not sure if Barre is really underrated, but Tilbrook is an amazing soloist (as you noted) who rarely gets his due.
My Top Ten List of The Works of Mick Box : Favorite Songs and Performances from Uriah Heep’s Guitarist. »
My 2 favorite underrated are: 1. Bob Wooton (Johnny Cash) 2. James Calvin Wilsey (Chris Isaak first 4) Both have a great tone.
A guitarist's guitarist, Davy Graham, who should be a household name. Slighted by some critics for his vocals, I'll take him over Bert Jansch in both categories...