These are a few that seem to always be on heavy rotation for acoustic guitar on my system:
Doc & Merle Watson "Doc Watson & Son" & "Lonesome Road" - Bluegrass
Nitty Gritty Dirt Band & various artists "Will the Circle Be Unbroken" - Bluegrass
Muddy Waters "Folk Singer" (find the MFSL) - Blues/Folk
Buddy Guy & Junior Wells "Goin' Back to Acoustic" - Blues
Eric Clapton "Unplugged" (MFSL) -Blues
Cat Stevens "Teaser & the Firecat" & "Tea for the Tillerman" - Pop
Acoustic Alchemy "Natural Elements" - New Age Jazz
Dave Matthews & Tim Reynolds "Live at Luther College" - Rock/Alternative
Leo Kottke "6 & 12 String Guitar" - Folk
John Fahey "The New Possibility: John Fahey's Guitar Soli Christmas Album" -Seasonal
All are still available on vinyl, with the Muddy Waters and the Eric Clapton recently getting the MFSL One-Step UltraDisc 45 rpm treatment. Those two are absolutely phenomenal records. The others are also great both musically and performance-wise. Enjoy the music!