Tube rolling Question

Hello Tube Rollers
I recently bought my first tube preamp (Blue Circle 21.1). I've noticed I am need of new tubes as the tube whoosh is considerably more noticeable now than 6 months ago. The amp comes with  Electro-Harmonix 6sn7 tubes which I appreciate and dig the sound. I will certainly replace these with a the gold pin model as I like the sound profile. Here's my question:

What other tubes might you recommend for a different "flavor" of sound, and just to have fun with. I am a poor audio guy so please no recommendations for tubes that will cost more than preamp. 

Thanks in advance. 
I consider spares indispensable.  I just hope my spares stash outlasts me.  I'd hate to have to miss a mortgage payment(proper priorities, and all).
Be very careful of any seller that sells "NOS in white boxes". What this usually means is that the tube tests as NOS but is most likely used. I am not sure if one respondent was suggesting that there exist 6SN7s that were made by Amperex but just for the record Amperex never made a 6SN7. I have seen Amperex branded 6SN7s but these were made by GE. Be very careful of tubes branded Sylvania Bad Boys. The Bad Boy is a great tube but is very specific in construction. Tall, 3 hole black "T" plates with bottom foil getters. Most I have seen were made in late 1951 and in 1962. This is the only Bad Boy made and many ebay sellers are selling Sylvania tubes as Bad boys which are not and quoting an online tube seller who knows (or should) better. Be careful.

An excellent inexpensive 6SN7 tube is the GE short bottle, side getter. Read what Brent Jessee says about them. He makes a comparison to an extremely pricey tube. A friend has a Blue Circle preamp and uses that GE as it was his favorite from all he tried.

Great guidance and directions!!! Thanks One and all. You've given me a lot to look in to. 

Much Appreciated

Happy listening !
I have a pile of 6SN7GTBs as my amp (uses one) and preamp (four) use 'em. From new Tung Sols (these seem to require some break-in but do eventually sound reasonably neutral) to NOS GEs, Sylvania "chrome domes," possibly re-badged Amperex tubes that still sound fabulous (my Dennis Had amp was supplied with one of those and yeah...its internals are exactly like other non Amperex tubes) etc, and they're all relatively inexpensive and plentiful. You simply have to experiment to see what sound floats yer boat.