There is a local guy in Seattle who records under the name The Sight Below that I've really been digging lately. Its close to stars of the lid and other ambient music but with more of a shoegaze vibe. This track always blow my mind:
http://www.youtube.com/watch?v=-YwZNfjJ15U
Its basically just the same simple guitar part looped over and over with increasing amounts of reverb and feedback...simple but effective. Though his previous albums had more keyboards and drum machines, his latest one, It Falls Apart, is mostly guitar...
Emeralds, and their guitar player Mark McGuire's solo stuff, is mostly very clean looped guitar that is layered until it becomes a giant drone...
http://www.youtube.com/watch?v=Fabt4-UyvM8
Masterati is a recently defunct band that features layered looped guitars with hard driving rhythm section... a lot heavier than most of the other looped guitar stuff that's been recommend. Easily one of the best live bands I have ever seen.
http://www.youtube.com/watch?v=UKSRvqnrajQ
Early examples of looped guitar that I really like are Ash Ra Tempel's Inventions for the Electric Guitar and the Brian Eno/ Robert Fripp collaborations (which is the first example of live looping that I'm aware of).
I am done nerding out now....