4. Marvel (The Avengers)
Marvel, one of the world's high grossing companies in TV and film history and their ongoing success, in the form of hit movies and programmes, has all been devised from the great Stan Lee. The Marvel universe is notorious for having its fair share of crossovers and the Doctor, in his fourth incarnation, has even been in a Marvel made comic book. If the Doctor was to ever be featured in an on screen Marvel crossover, though, then the Avengers would be the most ideal place for him to start. The Doctor
is an avenger, in a sense. He protects the world (including many others) and he will do so until his last breath. Let's face it, a big screen blockbuster in which the Doctor and the Avengers team up to fight Thanos and the Daleks is something that every fan would pay to see. The trouble with this crossover would come down to the salaries. This would definitely be one of the highest budget movies of all time so the cast would want an excessive amount of money to take part. Stuff like this doesn't come cheap, you know.