Challenge accepted: Perfect Casts - OTTOMH

This is pretty difficult. Bear with me as I'm gonna go long as I do this off the top of my head....OTTOMH (a new list genre!). Some of these will be pretty obvious.

Champion:  (Personal favorite, most obvious, but try to prove me wrong)  What's Up, Doc?

Any movie that introduced Madeline Kahn to the world would make this list, but as Eunice Burns? And give Barbra Streisand those lines and that hat? And then add Austin Pendleton, Kenneth Mars, Randy Quaid, and Boss Hogg, and the guy who plays Judge Maxwell, and even your head waiter, Rudy? And, uh, ahem, Ryan O'Neal?  Perfect.

Here's a list of 21(!) movies (sorry, couldn't stop), in no particular order (after 1 & 2), that I can't think of a character I'd recast:

1. Casablanca
2. Harold and Maude
3. Moonrise Kingdom
4. The Fabulous Baker Boys
5. Gosford Park
6. The Grifters
7. Anatomy of a Murder
8. Out of Sight
9. Jackie Brown
10. Tootsie
11. The Big Lebowski
12. Passion Fish
13. A Mighty Wind
14. Dirty Rotten Scoundrels
15. American Splendor
16. Nine to Five
17. Notorious
18. Murder by Death
19. Jaws
20. Bull Durham
21. Ghost World
 
Looking forward to comments!