I've done the same thing. I don't even bother with the airstones, I just run a long piece(s) of airline for bleed.
No doubt airstones are a great muffler though!
Lots and lots and lots of choices really. For powder, my fave is Salty Shrimp gh+. For liquids... well, there's an abundance to choose from.
Which are you interested in?
Going off fish shows, they auction the aquapets off after the show and the club gets the proceeds to help offset cost and if any is left over- as seed money for the next one.
I haven't seen any discussion regarding this yet for this shrimp competition.
What's your price range? I have an Alita and love it. I know they have the smaller one (the AL-6A). Dependable, but costs more. It has a linear piston push.
http://www.kensfish.com/aquarium-supplies/air-pumps/alita-al-6a-linear-air-pump.html