I agree with nexttothemoon, both optionsxpress and thinkorswin are great. Both have great charting tools, but I chose thinkorswim because you can download the trading platform and because of this, It has more features and other interesting tools.
optionxpress charges $9.95 and thinkorswim $5 per transaction. Both have demo versions and I would advise you to try both and take your decision based on your preferences.