Years ago I started out with Lind Waldock - I had a great broker, but unfortunately, he needed to make a living too, so I was unable ever to get a real break on commissions. But my experience with Lind was very very positive.
Today, I trade through both Interactive Brokers and (due to IB's increased day trade margins) I have also started trading through Infinity Futures, and introducing broker to Transact Futures.
I have been very pleased with Infinity thus far - I've been trading with them since November 2008. Nearly all of my day trades are now conducted through Infinity.
As far as currency futures go, I trade primarily the Euro, though I occasionally trade the Pound, Swissy,and Yen.
Best Wishes,
ddaytrader