It really depends on what kind of tea you are looking for, you are
pretty much on for most teas with upton and specialteas.
Houdeasianart.com is a great place for Oolong and Pu-Erh teas. If you
can put up with a three week wait then yunnansourcing on e-bay is your
best bet for selection for Pu-Erh teas in general, and their
Bi-Luo-Chun premium is a steal for the quality. Enjoy your tea
adventure, and always keep an eye open for local merchants - nothing
beats sitting down and sampling a tea before you buy, though that is
something you find mostly from asian sellers.