The Renaissance Heathrow has a "buy one-get one free" offer on weekend rooms. Availability seems to cover most weekends from now through the summer. This is significant if travelling with family or friends, as although this is not a bad hotel (I prefer it to the LHR Marriott), the rooms are very small and are limited to one or two persons max. The rate is £70 per night for both rooms (£35 per room), must be in the same name and for the same night and does not include VAT or breakfast. There is no special code - it turns up with a routine search. London regulars will know this is an excellent deal, especially in the summertime. If you're MR Elite be sure to ask for an airport view... you can't get any closer unless you're on a plane.