The way postdocs are paid depends on their title code, and this affects their tax situation. The UCSF Office for Postdoctoral Scholars has an excellent page on title codes for all UC postdocs.
Free Tax Preparation
MyFreeTaxes.com provides free tax-preparation services to taxpayers who earned a "low" income. This value changes each year, but most postdocs will fall into this category. There are two ways to use this service. You can do this online via the provided H&R Block software. Alternatively, there are locations in Orange County where you can go and have an IRS Volunteer help with your tax preparation. An appointment is required. Visit MyFreeTaxes.com for more information.
International postdocs are not eligible to use the online service noted above with H&R Block. Postdocs may instead do it in-person at a location in Orange County. An appointment is required.
Another website international postdocs may want to use is Sprintax. This is a paid service that is specific for non-resident postdocs and takes the hassle out of figuring out tax deductions and tax treaty exemptions.