I have begun developing a R wrapper for the FRED API. It is hosted on GitHub at: https://github.com/mikeasilva/fredAPI. You will need to sign up for a FRED API key to use the wrapper.
Let’s say you want to pull Annual Real Gross National Product. Here’s how you could do it:
> fred <- fredAPI()
> fred$key('My FRED API key here')
> xml <- fred$series_observations('GNPCA')