One recent problem I've encountered: How to determine the right number of federal tax withholdings. Too many, and I have to write a big check in April. Too few, and I get to loan the government my cash all year, interest-free. Thankfully, I've found a simple withholding calculator you can use to refine that number.
Surf over to Kiplinger, where you can use their Easy-to-Use Tax Withholding Calculator to figure out the right number of withholdings in about 30 seconds.
To make it work, you'll need your completed 1040 (I used last year's, since my financials haven't changed much). Enter a couple of numbers, and bag! You get a recommendation on how to change your withholdings to prevent letting the government hang onto your cash for free.