James Franco and his Asian pillow doll, Kamiko, or something like that, was pretty funny.
I loved the cream colored cameo Tina would wear on certain episodes when she wore sweaters.
James Franco and John Hamm
Least favorite: Matt Damon
Rachel Dratch's Barbara Walters was absolutely brilliant ("Your father Werner, a burger server in suburban Santa Barbera..."), and so was Margaret Cho doing Kim Jong Il the first time.
The second time Margaret Cho did Kim Jong Il was terrible, however.
Best: John McEnroe, Brian Williams, Andrea Mitchell, Padme Lakshmi, Kellan Lutz, Whoopi Goldberg
Worst: Oprah, Kelsey Grammer, Condoleeza Rice
It's more recurring character than cameo, but I liked most of what Chris Parnell did as the "doctor."
Sheryl Crow and Adam Levine were funny as Jack's "European" friends.