well..sorta depends on what you like if you have an idea there? greener oolongs..darker..etc..
Adagio obviously has some oolong samplers..but if you are wanting to branch out already heres a couple suggestions from me..i am sure you will get many others
firstly..you can check the vendor topic if you havent already..all of those have been recommended by someone here. http://www.teachat.com/viewtopic.php?f=60&t=11932
if you dont want to wait a long time for shipping from china you can try something like seven cups based here in the usa. i ordered their rock sampler and found it quite nice. they dont have much real dark roast but more light and medium yancha's
if you want to try Taiwanese high mountain you could try floating leaves tea based in seattle. ive ordered from them before and had good results. They have a couple sampler sets too.
beyond that thanks to Entro there is jas-etea that basically resells stuff from yunnan sourcing. I have ordered a bit of Pu from their and am really enjoying that..so they also have a nice selection of oolongs there..also "local" in the usa..so fast shipping
just a couple suggestions for you