I really like Floating Leaves in Seattle. http://floatingleavestea.com/ Shiuwen, the proprietor, tends to get things with good body and often a touch more oxidation than some other sources. I will not say that her stuff is the best in absolute terms, and like any source, can vary from season to season (haven't had any of the 2012 winter season oolongs yet), but her choices tend to to match my personal tastes well, at least in terms of greener oolongs. She is also very responsive, and will usually give a very honest opinion of a tea if you ask. I think the pricing is fair for the quality, and usually there is some quantity discount as well.
Hou De is also a good source, and I think while he's been putting less stuff up, the quality of his Taiwan oolongs has actually gone up slightly in the last year or so.
Stéphane Erler, of http://teamasters.blogspot.com/ has some good items. The prices can be high, though I think not impossibly so.
Some folks have had good luck with Teahome (http://www.teahometw.com/), which ships direct from Taiwan. You can get the non-Ebay prices sometimes if you email them directly. I was not blown away with the one thing I tried of theirs, however, some people have had good experiences.
Edited by Will, 25 February 2013 - 01:49 PM.