For the last couple of months, I've been a subscriber of LoveFilm - basically for a few quid a month, they post you a rental or two and you just watch and drop it in the pre-paid envelope to send it back.
I'm on the lowest plan, but its handy - especially if you get caught with a night and have nothing to do!
Anyway, highly recommend - prompt service too.
Why not check it out :)
Go here for more info.