TurboTax sells the software needed to do fairly complex tax returns. If you have a very simple return (such as a Federal Form 1040EZ or 1040A), you can get it from TurboTax for free. Basically, if you just have a salary and a bit of interest from bank accounts and the like, you can do that for free.
https://turbotax.intuit.com/personal-taxes/online/free-edition.jsp