Choosing a discount broker for online stocks and options trading had been a challenging task just a few years back. I changed 4 brokers in the past before finally settling with Ameritrade.
Things have changed a lot in the last year or so and they seem to be getting better every day. The recent announcement from Bank of America to offer free trades for customers who have $25,000 on deposit has started a price war according to this USA Today article.
If you are still skeptical about free stuff here is a decent comparison review of 27 online brokers by Barrons. Some of them offer trades just under $5. Here is another recent review which actually splits the brokers in 3 categories: Premium, Full Service, and Discount. The last group is for us guys. :-)