Estimated tax on a one-time capital gain?

In 2010 I had a substantial capital gain that resulted in my owing more than $1000 when I filed my federal tax return. Fortunately I had withheld more than 100% of my 2009 tax and so avoided the underpayment penalty. My question is, what should I do in the future? I can adjust my W-4 to withhold more, but this... show more In 2010 I had a substantial capital gain that resulted in my owing more than $1000 when I filed my federal tax return. Fortunately I had withheld more than 100% of my 2009 tax and so avoided the underpayment penalty.

My question is, what should I do in the future?
I can adjust my W-4 to withhold more, but this gain was atypical (I sold a stock I had been holding for years when it shot up in price). I'd rather not overpay if I don't have to.

I know that estimated taxes are due quarterly. If I have a one-time gain in August, can I simply pay a 3rd-quarter estimated tax of 15% without paying estimates in the other quarters? And if so, is there a certain form I need to fill out with my tax return explaining why I paid that way?
Update: @B.L.O.C, in 2006 did you withhold 100% of your 2005 tax?
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