Sony were keeping their options open to cash in on a Spider-Man crossover, but their new reboot has proved enough of a success that they've decided not to cut the pie.
And speaking of Spidey, the Oscorp building was originally going to be in The Avengers, but the film was too far in post production to include into the movie.
A Runaways movie got as far as casting calls before they realized that it's just too complicated a mythology to dump into the franchise all at once (in the comics the plot ropes in time-travellers, mad scientists, aliens, crimelords, witches, mutants and pan-dimensional god-monsters, and that's just the origin), particularly before they'd even got the Avengers fully established. Of course now that they're brave enough to make something as obscure and bonkers as Guardians of the Galaxy it's safe to put it back on the "coming soon, maybe" pile.
The Wasp was initially going to be part of the team in The Avengers, and was even included in earlier drafts of the script. Joss Whedon is on record saying that he really enjoyed writing her, but ultimately had to cut her out of the script due to there being too many characters.
Of course, they recently reannounced the project for Runaways, and Wasp is all but confirmed for Ant-Man.
Then more comments came out that makes you wonder what comes first: Wonder Woman or Runaways, in film?