If there’s a Marvel movie, Stan Lee will show up in it. He’s had a cameo in just about all of them (his appearance in The Avengers is pictured above), and that includes Guardians of the Galaxy. He didn’t show up in the film as director James Gunn intended though. Gunn appeared on a couple of panels at Dragon Con, and Collider reports the following about Disney saying no to the initial plan for Lee’s cameo:
Originally, Gunn had planned to have Lee in one of the Collector’s exhibits. Groot would then look at the exhibit aghast, to which Lee would flick off the large tree creature.
I can see why Disney nixed that scene, but I think it’s a better idea than the cameo we saw.