You can use the free version of TurboTax at http://turbotax.intuit.com/taxfreedom/ through the Free File program (check IRS website for eligibility requirements.) Last year I used H+R Block's free online filing app, and every year before that I had done my return by hand (very simple, because they were summer jobs during high school and college.)

This year, I almost threw in the towel and opted to pay the $100 to have a CPA do it all, because I had so many lifestyle changes (graduating from college, no longer being a legal dependent of my parents, and working full time) and income changes (HSA savings, 403b savings, freelancing profits). But the free TurboTax seemed to accommodate them very well, addressing each matter in detail. My return totaled about $1,100!

A lot of tax prep shops have a deal where they review up to 10 years of previous returns for errors, and for deductions or credits you didn't take, and will file corrected returns. I plan to do that a few years from now, in 2010 when I'm 26 and have paid taxes a full ten years.