Interactive Brokers - $0.005 per share, minimum $1.00 per trade
MB Trading - $0.01 per share, minimum $1.00 per trade
I use MB Trading. There are no hidden or monthly fees. They offer you a trading program (no charts, but Level 2 included) and Medved Quote Tracker (a simple charting program). You can integrate their trading program into different leading charting programs (like eSignal or QCharts, if you can afford them). This board seems to be dominated by IB people, and that's cool - I just started with MB, and the difference in commissions isn't big enough to relearn a new platform.
Most direct access brokers, in fact I think all of them, charge a penny a share or less. Online brokers like Ameritrade charge $9.95 per trade, Scottrade $7 per trade, ShareBuilder (only for long-term buy and hold, since they only put trades through once a week) $4 per trade. I think TradeKing is $4.95 per trade, and E-Trade is somewhere around the $7-10 per trade area. In my opinion, there is no good reason to use an online broker - they have prettier websites and more bells and whistles, with some decent research, but they're slower in execution and far more expensive.