Some favorites of mine that didn't make the list.
-Clegg from Eastbound & Down
-Eel O'Brien/Plasticman
-Max Fischer from Rushmore
-Tammy Metzler from Election
-Seymour from Ghost World
-Maude from Harold & Maude
-Sylvester from It's a Mad, Mad, Mad, Mad World and Lorenzo Saint Dubois from The Producers (both played by Dick Shawn)
-Lenny Pike (Jonathan Winters) from It's a Mad, Mad, Mad, Mad World
-Loady McGee and Sinus O'Gynus from Angry Youth Comics
-Reed Rothchild (John C. Riely) from Boogie Nights
-They guy who is trying to sell a piece of John Wayne's bath tub in Taxi Driver
-Pee-Wee Herman (how did he not make the list?)
-On the Pee-Wee tip, I'll add Francis and Captain Carl
-Deputy Andy from Twin Peaks