I'll refer you to Sports Night.
Also from Andrew Sorkin...
• Joshua Malina: Jeremy Goodwin (Sports Night) / Will Bailey (The West Wing)
• Janel Moloney: Monica (Sports Night) / Donna Moss (The West Wing)
• Felicity Huffman: Dana Whitaker (Sports Night) / Ann Stark (The West Wing)
• Clark Gregg: Calvin Trager (Sports Night) / Mike Casper (The West Wing)
• Timothy Busfield: Director (Sports Night) / Danny Concannon (The West Wing)
Ah. I should've said "other than shows where Aaron Sorkin was involved" :)