Free site with current and historical rates. Lets you generate a table showing exchange rates with almost 70 countries with one query.
Nominal vs. Real
Virtually all of the sources here present nominal exchange rates, meaning they only the rate at which currencies exchange, ie 1$ = .75£. Real exchange rates are adjusted for inflation and other differences in prices. More information can be found in this article from the International Monetary Fund(121k PDF)
The IMF is the only online source available at the American University for time series data on real exchange rates.