Just a short reminder that the final 2009 Estimated Tax Payment is due January 15, 2010. To avoid (further) penalties for underpayment of estimated tax, in general, by January 15, 2010 you should have paid (in combination with 2009 US taxes withheld and all other 2009 Estimated Tax Payments) the lower of:
1) 90% of your (eventual) 2009 tax liability, or
2) 100% of your 2008 tax liability (110% if your 2008 Adjusted Gross Income exceeded $150,000)
Note: You do not need to make estimated tax payments if your final 2009 tax liability does not exceed $1,000.
You can find the form and instructions at: http://www.irs.gov/pub/irs-pdf/f1040es.pdf