Here are the big ones: - E-TRADE Financial Corporation ETFC - Interactive Brokers Group, Inc. IBKR - The Charles Schwab Corporation SCHW - TD Ameritrade Holding Corp. AMTD - optionsXpress Holdings, Inc. OXPS Go to google, type in their tickers and look at related companies. Plus there are investment banks like GS and MS that obviously do brokerage... clearing firms like Pension.... market makers like Knight Capital etc.
For more firms look at the holding of ishares ETF IAI and weed out the investment manager companies and exchanges. http://us.ishares.com/product_info/fund/overview/IAI.htm