Depends if you want a blow up one, fold out one or what...
We have a ReadyBed blow up double lilo thing. Its suprisingly comfortable, easy to inflate with a pump from Argos, and folds down into a small bag to store. The down side is it makes a rubbery noise when you turn over on it, I think from rubbing on the floor, and lots of people are too wriggly for lilo's!