For most investors, the arms race among the online brokers may seem like overkill. The exploding array of choices and tools offered by many firms now greatly exceeds the need or grasp of many investors.

Low trading commissions, easy-to-use interfaces, and a broad range of educational materials are almost always all that is needed. With that in mind, here are six basic online brokers that should more than satisfy the needs of most investors.

TDameritrade.com

This firm has been so successful that its founders were able to buy the Chicago Cubs baseball team in 2009. The key to their success is their ability to stay one step ahead of the pack. Ameritrade (before it was bought by Toronto Dominion Bank) always offered low trading commissions and a straight-ahead no fuss trading platform.

Rivals eventually copied that approach, and TDameritrade stayed one step ahead by acquiring thinkorswim.com in 2009. Thinkorswim had become a leading player in the world of options trading, and by coming together, Ameritrade can now offer the most robust options trading platform among the plain Jane online brokerage sites.

Need to know: All stock trades are $9.99. A basket of no-commission ETFs, no-load mutual funds cost $50, options trades are $10 plus $0.75 per contract, U.S. Treasuries cost $25 per trade, futures are $3.50 per contract, margin interest ranges from 7%, depending on balances. The website also offers a wide range of third-party research.

E*Trade.com

Along with ameritrade, E*Trade has been very popular among retail investors. The company had a financial scare in 2008 thanks to an ill-fated move into mortgages, but is now on more solid financial footing. E*Trade is seen as a technology innovator, continually rolling out new features to exploit the latest trends. For example, E*Trade was an early developer of trading platforms for smartphones and is quickly establishing a strong presence among iPad users.

Need to know: Fees are roughly similar to Ameritrade's noted above. The company's Power E*Trade pro offers a very comprehensive set of analytical and trade execution tools. E*Trade operates 30 retail branches around the country to help investors get started.

Fidelity.com

Over the last two years, investors have made a very big push into exchange-traded funds (ETFs) which are like industry or country-targeted mutual funds but without the costs associated with fund managers. In response, major fund managers are trying to get in on the ETF action in a big way. Fidelity has established a comprehensive set of ETF research tools, and even offers a few of the most popular ETFs without any trading commissions.

Need to know: In a bid to steal market share, Fidelity undercuts key rivals on price, offering $8 stock and options trades (each option contract costs an extra $0.75). U.S. Treasuries can be bought for no cost (online only), while other bonds cost $1 each (per $1,000 increment). Offers more than 1,000 mutual funds that carry no trading costs. Margin interest rates are slightly lower than key rivals.

Vanguard.com

Vanguard has long insisted that investors should avoid paying onerous fees to high-powered fund managers, and instead thinks that low-cost passive funds are the way to go. So it’s no surprise that Vanguard is a proponent of low-cost company-sponsored ETFs, offering 50 of them without commissions. The site offers suggestions on how to tailor a basket of ETFs to provide the right mix of risk and reward, depending on your age and investor interest.

Need to Know: Like Fidelity, Vanguard is seen by many investors as a mutual fund firm rather than as an online stock broker. So Vanguard also offers very low commissions, starting at $7 for smaller accounts (though after 25 trades, that balance jumps to $20, unless you have a balance of $50,000 or more) and working down to $2 a trade for investors with more than $500,000 in assets. The real appeal is for investors that mostly trade ETFs and funds (presumably through Vanguard’s own offerings), and only a modicum of direct investing in stocks.

Scottrade.com

If you like the choice of face-to-face discussions with an online broker representative, then you'll love Scottrade, which operates 505 retail branches across the U.S. The company believes that it typically achieves the best possible price for clients -- better than most other online brokers -- though we have no way of verifying that claim.

Need to know: The firm offers $7 stock trade commissions, but other trading fees are slightly higher than the peers. For example, you’ll pay $7 per ETF (no freebies here), and $1.25 per option contract on top of the $7 fee. At just $500, Scottrade has among the lowest initial opening costs in the business.

Merrilledge.com

Merrill Lynch came to realize that key clients were starting to manage some of their own investments on the side, taking advantage of much lower commissions found elsewhere. To lure those assets back, the firm launched merrilledge.com in 2010. The site's fee structure is in line with the rest of the group. As an added kicker, clients gain access to Merrill Lynch research.

The move is the result of Merrill's acquisition by Bank of America. A typical BofA client isn't used to the high costs and services of a full-service broker. In a risky attempt to keep the habits of its distinct client bases from changing, BofA clients automatically get access to merrilledge.com while Merrill Lynch clients have to be lucky enough to have heard about it and know to ask for it.

Need to know: Clients can make up to 30 free trades per month, as long as they maintain $50,000 in their account. Option pricing is similar to rivals, but if you need to conduct a trade over the phone, Merrill's fees quickly add up. In my mind, the main reason to open an account here is to gain access to Merrill Lynch research, although it's not clear how much of the firm's global research is available.

Honorable Mentions:

Less well-known sites offer trading commissions at even deeper discounts. For example, junotrade.com offers $5 stock trades and options trading commissions that are among the lowest in the business. The site also offers a set of tools that allows investors to test how their investment strategies would have fared if deployed, known as back-testing.

Zecco.com and Lightspeed trading also offer very low commissions and have garnered high customer service reviews in recent surveys.