Nick Drake and others like him

have a listen to Tim Buckley..
unique voice most times amazing.Albums/cds: Goodbye and Hello, Dream Letter,Live at the Troubadour 1969. Later music gets a bit avantgard.His guitarist Lee Underwood was also great.He was the father of Jeff Buckley..unfortunately both committed suicide at an all to early age.
You also might like Richard Thompson either solo or with his early group Fairport Convention. HTH

go straight from nick to john martyn (actually a friend of nick's)...would highly recommend starting with 'solid air', 'one world', 'grace and danger'...a singer, songwriter, guitarist for the ages....

Nick always reminded me of a quieter version of Donovan, there's a few 'best of Donovan' discs around.

Another one would be Robert Wyatt 'Rock Bottom'. It got 5 stars in 33 reviews on Amazon:

http://www.amazon.com/Rock-Bottom-Robert-Wyatt/dp/B000006AXS

Someone more recent - equally as unique who has unfortunately passed on as well - Chris Whitley. Perhaps 'Dirt Floor' might be a good start, however do yourself a favor and spend some time exploring his other offerings as well.

definitely Elliott Smith (S/T, either/or, XO). also try Bonnie 'Prince' Billy's 'Master and Everyone'. but in the end, Nick Drake remains unique...