Amazon have the Microsoft Natural Ergonomic Keyboard for a penny under 18 quid. The RRP is £50, and this is a very good keyboard for the money. I run one in the office and at home and find it very very comfortable - you'll have to get used to having a split keyboard though - it doesn't really suit non-touch-typers.
4/5* average customer review. Great price for a good quality ergo keyboard. I've run microsoft hardware for years and always found it top knotch. The kb itself is USB