Go for the 80GB console mate, best of the 3.

The Arcade comes with 512MB memory.

The Pro comes with 80GB memory and (I believe) the HD DVD drive built in for better DVD viewing.

The Elite comes with 120GB memory.

I had a 20GB and never used it tbh. The memory is only really for downloading games/movies from XBOX Live, which I never did as if you fill the hard drive you will have to delete your paid for games!

You can buy the 20GB hard drive for £40, which is the price difference between the Arcade and the 80GB Pro console.