The first DVDs we bought were strap on (ooer missus) jobs from Halfords, they had one DVD player and two screens, they worked fine, but they got ruined because the cables kept on getting pulled out, and the screens were a poor fit on the headrests.
I then bought some DVDs/Screens that are integrated into the headrests from Ebay, they are a lot neater as all the cable run inside the seats, so there is nothing that can be pulled out, there is also a DVD player in each headrest, so there are no arguements over what to watch. They came with game controllers and games, but they were pretty poor and some of the language in the games was interesting, so they were binned. They were just cheap unbranded units, but they are now 12 months old and still work great, the headrests are a universal fit, but I had to buy adapters to fit our seats, they do rattle slightly if there is no one sitting in the passenger seat.
If you do a search on Ebay there are loads available.