Here is another thing one should know about firms like TD Waterhouse/Ameritrade, Scottrade, Etrade and its ilk that charges per transaction as opposed to per share like IB and Light Speed.
Firms like TD Ameritrade are not really direct access firms. This means that once you place an order it does not go directly into the Market to buy or sell your shares. Your transaction goes to a person in the Trade Approval/Support Department to get approved before your order gets executed. That is why your order takes a few seconds to execute. During this time your order gets "worked" on by the firm's traders. Especially if you put a Market Order in you are being fucked over. It is legal by the way too which is a slap in your face. Also you are paying some $7 to $10 per transaction. In today's pricing that is mighty expensive. It maybe cheap in the 90s but in today's market you can get much cheaper like 30 to 60 cents per 100 shares. It you are a heavy volume retail trader it goes as low as 15 cents per hundred shares.