The undisputed leader in online trading, Interactive Brokers offers the best and cheapest solutions for investors and traders worldwide. Commissions get as low as $1 per trade, depending on the exchange and product you are trading. IB offers stocks, options, warrants, bonds, futures, forex, funds, etfs and many others, on exchanges in US , Europe (almost all countries), Asia (Japan, India, Hong Kong, Singapore, Korea) and South America. The catch is, that you need a minimum of 10 000 USD to open an account.
The company also offers master account solutions for hedge funds and advisors , through which they can manage their clients. I myself have an account with IB simply because they are the best and cheapest. I also manage some of my clients through here, as it offers a safe and convenient way for funds management.
Schwab is a relatively old company, which offers online trading for stocks, options, bonds and mutual funds. Their fees are sometimes higher, but you can open an account with as low as 1000 USD. The good thing is, that they also offer stock markets in Hong Kong, Japan, Canada, UK and the rest of Europe.
3. Saxo Bank
The Danish bank emerged as a leader for European retail investors, offering a lot of exchanges at affordable prices. You can trade all European and North American stocks, plus Singapore, Hong Kong, Australia, Tokyo. The company offers stocks, bonds, forex, futures, options, CFDs and funds. You also get lower commissions if you trade more frequently or deposit a large sum in the account.
4. Fidelity Investments
One of the largest investment companies in US, Fidelity has a wide range of products in nearly 25 countries and 16 currencies. You can trade stocks, funds, options and bonds in North America, Europe, Hong Kong, Japan, Singapore and South Africa. Fidelity is definitely one of the cheapest brokers out there, beaten only by Interactive Brokers.
Each broker has different commissions, and they might not accept customers from certian countries. So check individually before you open an account, to find the best one that suits you.