If you are planning on selling an investment on which you have a gain, it may be best to wait until after the end of the year to defer payment of the taxes for another year (subject to estimated tax requirements). 

If you are due a bonus at year-end, you may be able to defer receipt of these funds until January. This can defer the payment of taxes (other than the portion withheld) for another year. Deferral of tax generally won’t work where the bonus is contractually due in 2007.

If your company grants stock options, it may be wise to wait until next year to exercise the option or sell stock acquired by exercise of an option. Exercise of the option is often but not always a taxable event; sale of the stock is almost always a taxable event.

If you're self employed, and can afford the delay in cash inflow, defer sending invoices or bills to clients or customers until the end of December.

Caution: Keep an eye on the estimated tax requirements.