So, I've recently started looking for good acoustic/instrumental artists (came across this while watching Simpsons, liked it), and I was wondering if anyone had any recommendations. Basically, something soothing, with guitars or classical instruments (probably no electric guitar, no other electric instruments). No heavy vocals. I like Mason Williams and Don McLean so far.

Jethro Tull. His most known songs will not satisfy you, but his Acoustic work is simply amazing. Stuff like "Pastime in Good Company" (but I couldn't find a good YouTube performance).
Jack Johnson.
Andy McKee.
Look for the soundtrack album "The Fountain" by Mogwai and Clint Mansell.

In fact, Candy Rat will probably satisfy you if you like Andy McKee: http://www.youtube.com/results?search_query=candyrat&aq=f

This was mostly for the acoustic part. Now, for instrumental, you must take a look at the post-rock, it's beautiful.
The best "applied" post-rock technique is made by Yndi Halda (their only demo-album can be found @ Pirate Bay).
But since I love 'experimental' artists, Godspeed are the best to me.
http://www.staredit.net/topic/10448/

There's also a phew good hits from the Gold Rock era. Stuff like:
Horizon - Genesis
Pigs on the wing - Pink Floyd
Wild Horses - Rolling Stones
Castellorizon - David Gilmour


As for the Classical Guitar era, go on and search for Fernando Sor and Carcassi.

Patrick Watson may also impress you, though he does use vocal. I recommend:
Weight of the world
Man under the sea
The great escape
Bright shiny lights

Give me feedbacks about my recommendations!

If you like jazzier stuff, nujabes is one of my favorites (not all of his stuff is instrumental though, but he makes quite a few.)
Counting Stars

If you like more hip-hoppy instrumentals, I personally like edIT.

Well, if we can go get some Jazz stuff, you may like St. Germain's album "Tourist".
If you liked stickynote's stuff, go on and search for Bonobo: he has some great music for you.

If you like bass try some Victor Wooten. I guess that counts for something right?

Here's a good soothing artist If ya don't believe me, try this on for size.

Apocalyptica. They cover rock songs, but they use cellos, so it usually evens out to something awesome.

Eric Clapton, extreme's More Than Words, anything from Adeaze. Look for people on youtube doing guitar covers of songs without singing them, then you get the guitar without the words if you don't want lyrics.

Drums are usually synth, and obviously the bass is electric. Béla sometimes drops his banjo and plays an electric guitar. Futureman occasionally switches from drumitar to drums.

Also an option: Stay classy (click both links).

I strongly recommend The Dodos.

Rockz, this bassist is amazing! O_O

says: Milow unplugged = <3

http://www.youtube.com/view_play_list?p=1E3888E3D60750E6

One of the songs of the play list for direct play:

he has 8 hands.

Here's a nice relaxing touhou remix. The rest of demetori's stuff is BALLS TO THE WALL METAL. I can't tell how the quality is on these speakers.

"They", not "him". Ian Anderson is "him".

I know a few people who really like Stanley Jordan, all of whose stuff I've heard is entirely guitar or at least instrumental. But I never really pay attention so I can't really say much more than that.