Just watched Fantastic Four (2015) (I smell yet another reboot...), and noticed that Stan Lee was one of the Producers. However, I didn't catch his usual cameo in a Marvel movie.
Did I miss it, or did he not play a part in this one?
There isn't one. From Entertainment Weekly:
In a new interview with Larry King, Stan Lee says he knows why [the 2015] Fantastic Four was such a flop: “It’s probably because I didn’t have a cameo in it.”
Lee, who created the original Fantastic Four with Jack Kirby, added that the filmmakers didn’t discuss the story with him. In fact, he still hasn’t seen it. King also asked him if he thought there were too many superhero reboots in too short a period of time, to which Lee replied, “That may be true.”
Fantastic Four was one of the few Marvel movies Lee hasn’t appeared in, as he’s made dozens of cameo appearances in Marvel movies and TV shows, from The Avengers to Agent Carter. He also appeared in the 2005 Fantastic Four as mailman Willie Lumpkin.
A minor character there (a technician) is called Stan, but that's about it.