All major brokerage firms provide their clients with on-line services, including trading platforms, latest market & financial news and research.
Customer need to select the site that is best for them. Traders have requirements in a site, while investors have other requirements.
Although most sites are geared to general securities and commodities, however customers may have special needs for the types of products they trade, and the markets in which they trade. For example I use Fidelity for investing. Scottrade for equities trading and ThinkorSwim for option trading
It seems that the most popular firms for on-line investing/trading all of which provide excellent platforms and services are; Scottrade; Chas.Schwab; TDAmeritrade; Fidelity; E-Trade and Thinkorswim. In your situation, you may be best served if you select Scottrade or Ameritrade
Becareful, some one thought Sharebuilders would serve your purpose, Sharebuilders is NOT for those that want to trade, the firm can not properly handle "trading" orders or trading accounts