You really can't beat Joe Pass, he fits any mood, season or time. Pure class.
I wonder if many round here know of Davey Graham? Well he is without question one of the greatest acoustic guitar players of all time, I'd rank him right near the very top. He was the first folk guitar hero for the British and acoustic guitar idol for a whole generation. His disciples include Bert Jansch and John Renbourn and Donavan and then slightly after came John Martyn, Richard Thompson, Jimmy Page and Nick Drake. You can also trace Neil Young's acoustic side to Graham through Bert Jansch. His most famous piece Anji has been copied by anyone and everyone and he also invented the DADGAD tuning. I'd suggest getting any of his early - mid 60's stuff, the way he combined world styles to Gaelic melodies puts him ahead of the rest. Sadly I can't find any good footage of him on youtube, I do have some great bbc video footage of him on tape. But what they do have is this weird clip of him playing when he was still a kid - about 18 or something:
Speaking of John Martyn as well, (dig the effects!) try this for size: