Stock Markets Exposed - Who is the cheapest online stock broker in the US?

Who is the cheapest online stock broker in the US?

Live in the US and would like to invest on the NASDAQ or DOW. who is the cheapest and has a online facility? Only really interested in EXECUTION ONLY

I think it is thinkorswim. They have a Per Share commission: $0.15 a share or $ 5.00 minimum. They also have a Flat Fee Trade: unlimited market or limit order trades (up to 5000 shares) for $9.95.
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