Most dividend and capital-gains distributions occur at year-end, so making a sufficient 4th quarter estimated payment by the January 15 deadline will eliminate the possibility of a penalty that might otherwise result from these year-end distributions. In other words, make a 4th quarter estimated payment sufficient to cover your overall tax liaibility when combined with your other tax withholding and estimated payments. However, you might need to annualize income on Form 2210 to avoid an underpayment penalty for the earlier quarters of the year. (You could still end up with underpayment penalties for the first three quarters of the year if your other tax payments were insufficient to cover the income in these quarters.)
Even if you don't have enough withheld or paid in estimates to cover your tax liability, if you meet any of the safe-harbors (see TomYoung's comment below) you won't have an underpayment penalty. Regarding underpayment penalties, see: http://www.irs.gov/taxtopics/tc306.html
