Hotelshop have a deal where you can buy a theatre ticket and get a hotel room for free. The deals start at £44.75 for Joseph but you can change your theatre show / date or upgrade your hotel for a little extra.
It looks like it includes most shows on in London at the moment.
Buy a top price ticket for Joseph and get a free night`s stay at a 3 star central London hotel with continental breakfast! This package is based on two people sharing a twin or double room. Offer valid for performances on Monday to Thursday evenings. Upgrade to a 4 star hotel from only £20 per person or upgrade to a 5 star from only £35