Free US interest rates historical data download

Hi

I've done a google search which threw op several possibilites - but has left me a bit confused .
I'm after a website address that will allow me to download historical data for US interest rates - preferably in Excel format. I am wanting the equivalent of the BOE interest base rate data - what is the US equivalent called? -(is this the Federal Funds Rate - the rates banks charge each other for overnight loans)?

Thanks a lot

jtrader.