Where was Stan Lee's cameo in Guardians of the Galaxy, or did I simply miss it?
Yes, Stan Lee did have a cameo in GotG.
On the planet Xandar when we first meet Rocket Racoon, you see him scanning the population with a pair of binoculars and making sarcastic comments
He notices Stan Lee who has his arm around the waist of a young woman. Rocket says ' Look at Mr Smiles over here, where's your wife old man! What a class A prevert'
So he did have a cameo just not a talking one.
He was one of the people Rocket was scanning when he and Groot were in the middle of the Xandarian city.