Taiwanese Pack 2.1
A simple input method editor for the PC, which also includes macro scripts for Microsoft Office to enable POJ functionality in Word.
FHL Taigi-Hakka IME (External link)
The best input method out there for Windows and Mac OS X, the FHL IME allows you to type Hàn-lô or pure romanization, with both POJ and Tai-lo supported. It also offers the ability to type in Hakka (another Chinese language in Taiwan), both in mixed character/romanization script or pure romanization.
Taiwan's Ministry of Education IME (External link)
Inputs for Tai-lo, the romanization that the Taiwanese government supports. Versions for Windows, Mac OS X and Linux. The page is in Mandarin characters, but can be puzzled out quite easily if you don't read Mandarin. This IME will automatically convert POJ, TLPA and Tong-iong to Tai-lo as you type.