The Adventures of Baron Munchausen: the Game.
It could certainly allow for a nice replacement to Monkey Island as a comedic adventure series, but with a more . . . heroic hero than good ole Guybrush, which allows a completely different sort of humor and character than Monkey Island. I don't think they should be strict retellings of his adventures, but as they have done with established series -- new adventures in the mold of the old ones.
Arsene Lupin: the Game.
Much less over-the-top, Lupin's very fit to an adventure game setting -- something just barely touched upon by Frogware's Sherlock Holmes games.
Something involving conspiracies: the Game.
I don't know. Majestic-12, Mothman, aliens, stuff like that. That'd be interesting, especially if done as a homage to '50s sci fi shows like the Outer Limits. But that's already sorta been touched upon with S&M: The Devil's Playhouse.
Spy fiction thing: the Game.
Who else imagines Telltale making an adventure game where you have to escape a death trap laid by a Bond-esque villain using only stuff in the room and your inventory? I can!
The Goonies: the Game
SLOTH. LOVE. CHUNK!
The Spirit: the Game
The episodic nature would be perfect for this highly influential comic book hero.
The Mercury Men: the Game
If you don't know what the Mercury Men is, it's a really, really neat sci-fi show on the internet, split into 10 different episodes, each of about 7 or 8 minutes in length. Look it up if you like Indiana Jones and Star Wars, as they are both huge inspirations on the series.
Also, seconded on the Star Trek adventure game, for sure!