Here are a few discount brokers that we recommend. Currently we use Interactive Brokers, but we are very active in managing our positions, so this might not be your best option...
TD Ameritrade, charges $9.99 per trade for unlimited shares - market or limit orders. Clear and simple.
As of this writing, TradeKing offers market and limit orders for $4.95, and that includes broker-assisted trades. Currently they accept IRA accounts and have no minimums.
Investors starting with smaller amounts should consider to open an account with Firstrade, ChoiceTrade, or LowTrades. None currently have a minimum amount to open an account. And Scottrade ($7.00 market orders) requires only $500 to open an account at this time.
Investors making small trades should check out MB Trading where commissions can be as low as $1.00.
Active traders may want to check out Interactive Brokers. Their low commission rates may allow active traders to pay commissions as low as $1 for stock trades. The company provides many features useful to experienced traders, but the learning curve can be very steep for novice investors.
BUYandHOLD may be a good option for those that invest a set amount every month.