I think it's high time we had a thread like this.
First off, This site has a whole lot of things, mostly from spoken word samples. I'm not going to list them all but you might want to read through it.
Next, the relatively few I have spotted that aren't just common breaks, to my knowledge:
The opening bassline of Funky Acid Stuff - Honky Tonk Popcorn by Bill Doggett
The "get down and wreck shit" line from Reedin' - The Session by The Roots
The "we interrupt this program of dance music" from My Style - War Of the Worlds by Orson Welles
The "step up front" from Registarse - Bumpin' Bus Stop, don't know who it's by but I've heard that sample elsewhere
The "please mr groove" and "can you feel it" from Sparky is a Retard - Mr. Groove and Can You Feel It. Thank you google.
The vocals in A Fine Line are from The King's Singers doing two covers.
I think the beginning of Memory Towel is from Buffalo Girls.