UPDATE; extended through to 02 March, 2012.
For a limited period, Adobe are offering 50-percent off Lightroom 3. Please follow the link here to find out more or to buy. The offer only applies to customers in Europe and finishes was 05 February 2012.
Update: Amazon UK are offering Lightroom 3 for just £95.00 inc VAT (£98.30 inc p&p for the boxed version), and cheaper than the above offer from Adobe.
Lightroom Beta 4 is available to try for free, but will expire when version 4 is formerly released. You will be able to update from v3 to v4 for a fee.