Spot foreign exchange (exchanges of foreign currencies) brokers - They do not charge any commissions because they make profits from the bid/ask spread quotes. On July 10, 2006, the exchange rate between Euro and United States dollar is 1.2733 at 15:45. The internal (inter-bank dealers) bid/ask price is 1.2732-5/1.2733-5. However the foreign exchange brokers or middlemen will not offer the same competitive prices to their clients. Instead they provide their own version of bid and ask quotes, say 1.2731/1.2734, of which their commissions are already "hidden" in it. More competitive brokers do not charge more than 2 pips spread on a currency where the interbank market has a 1 pip spread, and some offer better than this by quoting prices in fractional pips.
Liquidity - The liquidity of a market affects the performance of scalping. Each product within the market receives different spread, due to popularity differentials. The more liquid the markets and the products are, the tighter the spreads are. Some scalpers like to trade in a more liquid market since they can move in and out of large positions easily without adverse market impact. Other scalpers like to trade in less liquid markets, which typically have significantly larger bid-ask spreads. Whereas a scalper in a highly liquid market (for example, a market maintaining a one-penny spread) may take 10,000 shares to make a 3 cent gain ($300), a scalper in an illiquid market (for example, a market with a 25 cent spread) may take 500 shares for a 60 cent gain ($300). While there is theoretically more profit potential in a liquid market, it is also a "poker game" with many more professional players which can make it more difficult to anticipate future price action.
Software and gimmicky products that promise riches overnight typically have a very short shelf life. They may work for a little while, but ultimately they will fail you unless you know how to make adjustments to the software yourself. Instead of getting suckered into trading product scams you're much better off spending your time and money on your own education.
You're probably looking for deals and low prices, but stay away from penny stocks. These stocks are often illiquid, and chances of hitting a jackpot are often bleak. Many stocks trading under $5 a share become de-listed from major stock exchanges and are only tradable over-the-counter (OTC). Unless you see a real opportunity and have done your research, stay clear of these.