I’ll second Carlos Santana’s nomination as well.

Also, Bonnie Raitt. Killer slide guitar…
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Another guitarist in Terry’s league back at that time was Phil Keaggy of the band Glass Harp. Ted Nugent was quoted as saying "I don’t know what happened to that Phil Keaggy, he could have saved the world with his guitar" in Guitar Player Magazine.
When Jimi Hendrix was on the tonight show in the late 60’s, Johnny Carson asked him, "what does it feel like to be the greatest guitarist in the world?" Jimi responded with, "I don’t know, you’d have to ask Phil Keaggy".
Phil was an incredilbe player, and another one of the many overlooked guitarists.

Here’s a few others that don’t seem to get much recognition:
Jim McCarty – guitarist for Mitch Ryder Detroit/Wheels & Cactus
Steve Hillage – guitarist for Kahn, Gong, Mike Oldfield, etc.
Steve Hackett – Genesis
Eddie Phillips – The Creation (first to ever bow an electric guitar)
Tony McPhee – The Groundhogs
Dave ‘Clem’ Clempson – Colosseum, Humble Pie
Jorma Kaukonen – Jefferson Airplane, Hot Tuna, solo
Peter Kaukonen – Jefferson Starship, Hot Tuna, solo
Peter Banks – Yes, Flash, solo
Eddie Hazel & Ron Bykowski – Funkadelic & Parliament
Darryl Stuermer – played with Jean Luc Ponty, Phil Collins, etc.
Phil Manzanera – Roxy Music
Jeff ‘Skunk’ Baxter – Steely Dan
Randy California – Spirit
Uli Roth – The Scorpions, Electric Sun
D*ck Wagner – The Frost, Alice Cooper, Lou Reed, etc.
Steve Hunter – Detroit, Alice Cooper, Lou Reed, etc
Paul Chapman – UFO
Mick Box – Uriah Heep
Jan Akkerman – Focus, solo
Frank Marino – Mahogany Rush, solo
Walter Rossi – Charlee, solo
Adrian Belew – King Crimson, Frank Zappa, solo
Mick Abrahms – Jethro Tull, Blodwyn Pig, solo
Leigh Stephens – Blue Cheer
Kazuo ‘Flash’ Takeda – Blues Creation, Creation
Elliot Easton – The Cars, CCR Revisited
John Goodsall aka Johny Mandella – Brand X, Atomic Rooster, etc
Lee Pickens – Bloodrock, solo
John Nitzinger – Nitzinger
Larry Reinhart – Iron Butterfly, Allman Bros, Captain Beyond
Les Harvey – Stone the Crows
Stan Webb – Chicken Shack, Broken Glass, Savoy Brown
Phil Keaggy – Glass Harp,
Adrian Gurvitz – Gun, Three Man Army, Baker Gurvitz Army
Floyd Radford – Edgar Winters White Trash, Johnny Winter, Tin House
Tom Verlaine – Television
Dominic Troiano – Bush (Canadian band), James Gang, solo
Bob Welch – Fleetwood Mac, Paris
Ricky Medlocke – Blackfoot, Lynyrd Skynyrd
Harvey Mandel – Canned Heat, Rolling Stones, solo
Mike Pinera – Blues Image, Iron Butterfly, Thee Image, Ramatam, Alice Cooper
Kirby (no known last name) – Stretch, Curved Air. Stretch also toured the US as the bogus Fleetwood Mac in the early 70’s

Some great answers here, but I feel many of the guitarists mentioned are not overlooked at all…and are very well known and respected musicians. Especially when it comes to the likes of Ritchie Blackmore, Gary Moore, Peter Green, Peter Frampton, Stevie Ray Vaughan, Pete Townsend, Frank Zappa, Eddie Van Halen, Martin Barre, Jeff Beck, and Steve Howe. No offense to the people that mentioned them…but when have they ever been overlooked?

I could list many more guitarists that I feel are overlooked…but there’s a few anyways!
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Edit: Neil Giraldo Pat Benatar’s guitarist husband
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