We used lastminute.com and booked the secret hotel for london heathrow - it was fairly easy to tell it was the Sofitel and we paid £79 (I think) for a ncie room in a 5 star hotel which included breakfast (usually £21 pp) - having booked our parking directly with Meteor beneath the hotel we saved a packet on the published prices.
Would I use them again - yes - as long as I could tell the hotel.
It is also worth pointing out that lastminute.com's price is the price you pay, where as on other sites they add in taxes etc., to the final invoice.