They pretty much look the same but I did notice some slight differences. For one, the seats are darker. When you put the A/C to the coldest position, it says A/C Max. If you have a manual transmission, the shifting is a lot easier in the 2009 than the 2008. I think the gears also rev higher in the 2009. Other than that, they are pretty much the same.
The thing I like best about the Scion tCs are its safety features. The car kept me out of the ER when my Scion tC 2008 was wreaked. That's why I bought the same thing in the 2009 version.