They have said they are making spider-man 4 with or without Toby and that Sam is on board.

Toby has said he isn't sure if he would come back and that it would depend upon the script.

I would like to see the following villians eventually though.

Vulture
The Lizard
Carnage
Mysterio
Kraven the Hunter

I would also be interested in seeing the Man-Spider mutation of Parker which leads to the possibility of the Lizard being a huge part of the plot along with Kraven or possibly the Punisher.

I would like to see the Kingpin as well but they already stirred that pot with DareDevil.

Spider-man has so much depth in character and so many good villains to choose from that they could make 10 great movies if they wanted to.