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I use etrade. Minimum of 10k or you'll get charged quarterly (I think $40). Depending on how actively you trade, commissions are $13 to $7.

If you trade 15 or more times a quarter, they give you a nice Java-based trading platform which they call Power E*TRADE.

Limits orders have no additional fees.

I've been happy with etrade. The commissions could be lower (and they are at a few other discount brokerage firms).
 
We use Scottrade. They don't have holding fees and charge $7/trade. We've been happy with their service so far.
 
First Trade, because it holds one stock that my Sharebuilder account didn't seem to have. That's it.
I used to use etrade, but they claimed I didn't trade something when I know that I did. I left.
 
I've used Ameritrade (now TD Ameritrade) for about eight years and been very happy. I don't do anything more complicated than buying and selling stocks outright (4-5 trades per year), but Ameritrade's been good to me for what I need.
 
TD Ameritrade has $9.99 commissions, no minimum ($500 minimum if using electronic transfer to open account), no maintenance fees for a standard account. If you open an account with $2,000, you get 15 free trades. Margin and option trading requires a $2,000 investment.
 
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