dorkbotpdx.org - enough said - http://www.dorkbotpdx.org/wiki/pcb_order
traces down to 6mil, excellent quality boards, excellent customer serviceb. i have had probably 50-75 boards done by them for prototyping and they just work - no quality issues whatsoever. i have so far gone down to 0402 and 4x4x.09mm 24pin QFN and 3x3x.9mm 12pin LGA packages with no issues. haven't gone 0201....yet
if you are doing through hole boards it may get a bit expensive but they are US based and you get 3 boards which is excellent for prototype. i would have no issue using these boards in a production environment, they are just quality.
if you use eagle, you can just submit brd files and not have to worry about creating the gerbers which is nice if you are just getting into the board creation.
size comparison w/ a 6dof board w/ itg3200 and bma180 next to a micro sd card and as you can see, the board was not pushed hard for size as it did not need to be the smallest possible board:
i fly multirotors and these boards works excellent
hope this helps. they do a panel or ? every week
also, i am by no means associated w/ dorkbotpdx.org other than an extremely happy user of their boards. have 3 or 4 designs coming this i think