I've found a few while playing the game for the past 2 weeks(though I'm sure there's much more hidden):
-Sign's description:Read it(it costed me a victory in Arkantos' first real scenario of the campaign) =)
-Hippopotamus:There's one line in the description that is a joke...easy to spot =)
-FPH's description:Read it(it's a modified version of the hippo one) =)
-Lazer bear:Read it(I'm almost proud to be a Canadian when I see that superhero =p).
-Raft:Well, there's a monkey on it and the description is a nice poem written by monkey.
-Monkey:There's one line in its description that is a joke.
Though I'm sure there's more...found any ?