Hi Dave,
I think taking your Girlfriend away for Valentines Weekend to propose in incredibly romantic and I'm sure that after 11 years it will be a wonderful surprise.
But where to go?
I'd look at somewhere a little special - travelling on 15th Feb 2008 and returning on 17th Feb 2008.
I've had a look round for you and based your trip on flights from Gatwick, this can of course be changed to site your closest airport. and this may well effect the price.