I'm sure we could think of a few things still left to be sampled.
Nobody's done fingernails on a chalkboard yet, AFAIK.
How about old man sounds, you know the sounds we 50+ guys make when we sit, stand, bend over or reach for the remote.
How about the Sounds of the Miracle of Birth?
The Demolition Derby Percussion Set?
Tuned Dog Farts, the perfect accompaniment to the barking dog library.
Maybe celebrity sound bites. Somebody already got sued for sampling James Brown's grunts (jeez, how hard would it have been to put up a mike and go "ugh!"), so why not MIDI-mapped words of wisdom from the likes of Paris Hilton, Jessica Simpson (even better! Bart Simpson!) or those "real" New Jersey skanks?