This is my very own guess at what will be at launch. I will star anything that is my own logical guess on what we've found out so far.
At launch, apart from the various other merchandise that will be released, we know that there will be 40 other playable pieces to go with the game. So what are these.
Firstly, the Disney Infinity game is making its way out on Nintendo Wii, Wii U and 3DS, Microsoft PC and Xbox360 and Sony PS3.
Secondly, it has also been reported that there will be 17 characters at launch as well as 20 power discs, leaving room for 3 play sets. <----- it has now been verified that they'll be 20 characters total in 2013, not necessarily 17 at launch.
Characters (and their worlds):
Pirates of the Caribbean PlaySet - at launch
Captain Jack Sparrow (Starter Set)
Captain Barbossa (Single and Sidekicks Triple)
Davy Jones (Single and Villains Triple*)
Monsters University PlaySet - at launch
Sully (Starter Set)
Mike (Single and Sidekicks Triple)
Randall* (Single* and Villains Triple*)
The Incredibles PlaySet - at launch
Mr Incredible (Starter Set)
Mrs Incredible (Single and Sidekicks Triple)
Dash (Single)
Violet (Single)
Syndrome (Single and Villains Triple*)
Cars PlaySet - at launch*
Lightning Mcqueen (Playset)
Holly Shiftwell (Playset)
Mater (Single)
Francesco (Single)
Lone Ranger PlaySet* - probably July
Lone Ranger (Playset)
Tonto (Playset)
This leaves three more characters for one more PlaySet. This PlaySet will probably be the Toy Story in Space PlaySet that is being reported in a few places. This would make sense as a Buzz Lightyear game was being made as a successor to Avanlanche Software's own Toy Story 3: The Videogame, which is where the ToyBox mode originated, but it never saw the light of day.
This would make the characters, Woody, Buzz and Jessie, completing the 20 characters.
Just my thoughts, please feel free to comment on them.