What is your connecting flight or what airline are you taking? I know China Airlines offers a short tour around town. There isn't much to see around Taoyuan so you'll have to hop on a bus (or take a taxi) to Taipei. You should have around 4-5 hours to walk around so just go to the Financial District and snap some shots of Taipei 101 (the most expensive building in the world = it is shorter than the Burj Khalifa but it cost more because it's built on an earthquake fault and Taiwan didn't use indentured servants for cheap labor).