So far i have bought bananas from those sources:
http://palmscenter.de/ (2011)
http://www.bananen-freak.de/ (2012)
My experience was very positive with both of them.
I haven't had any interaction with the seller in both cases (i just ordered through the webshop). The plant were, in both cases, from what appeared to be tissue culture, well packed, shipped quickly.
For the next year i plan to order from:
http://www.bananenshop.de/http://www.gekko-enterprise.com/ (this one for international order)
So i can't actually comment on the quality of the plants of those two. I didn't had any interaction with the first one, but i talked quite a bit with the latter and he is a very nice guy, very willing to help, so i have nice expectations. Be sure, if you plan to order from the latter, to ask for his complete catalogue, since he has a very high number of cultivar for sale (more than 200), but they don't appear on the main page. Just remember to check for synonims.
Good luck!