Alright, my quick and dirty guide to on-line tea retailers.
http://www.specialteas.com/ - A nice domestic retailer for those starting out in the world of tea.
http://www.adagio.com/ - Same as specialteas above.
IMHO, these are the two places to start your tea journey. I should mention Teavanna here. Many love these folks, many order from them. I do not nor would not do business with them. I shall disparage no more than that apart to say price/quality is just not there. If you'd like me to disparage more, do it in PMs please.
Now, the next level, should you decide this tea thing is for you are the domestic premium tea retailers:
http://www.redblossomtea.com/index.php
http://www.puerhshop.com/
http://www.shanshuiteas.com/
http://www.sevencups.com/
http://www.theteagallery.com/
plus several more too numerous to mention.
I will say that these are good, quality vendors with quality teas. I will also say that I do not use them. I tend to order from China, Japan, Taiwan, etc., the source as it were.
Some of my favorites in this vein are:
http://www.houdeasianart.com/ (Yes, they're domestic, but Guang has access to some truly stunning teas not available elsewhere).
http://www.jingteashop.com/default.cfm My favorite oolong vendor.
http://www.yunnansourcing.com/store/ My favorite pu-erh vendor.
http://www.teaspring.com/ My favorite Chinese green vendor.
http://www.tuochatea.com/
http://www.teafromtaiwan.com/
http://www.teahabitat.com/store/ Another domestic, but Iman has the best Dan Cong oolong generally available.
http://teamasters.blogspot.com/
http://www.denstea.com/
http://www.o-cha.com/
and others too numerous to mention.
Should you find yourself far enough down the slope that this last group comes into play, check out
http://www.teachat.com/ , the Cigar Asylum of the tea world.
Hope this helps.