Miranda Cosgrove guest starred in an episode about a teen starlet going off the rails. It talked about the Contractual Purity of the real-life Disney stars and how they generally have to smash that purity into bits once they turn 18 to get work outside Kids TV even if it's not who they are inside, poked at Sloan being a No Celebrities Were Harmed version of Lindsay Lohan, and managed to be an Actor Allusion since Sloan was dressed up in a way that made her look like a grown up version of Megan as well as one episode where Carly Shay dressed up as a punk rock chick.
Vince Korsak is a blowhard lawyer who tries to throw a case- which would let him challenge DOMA on appeal- in 'A Defense of Marriage'.
Danny Blue appears in Season 4 as Kalinda's psycho husband.
Fake American: Scottish-born (now a US citizen) Alan Cumming playing Eli Gold. Also Londoner Archie Panjabi playing Kalinda Sharma (though her in-universe nationality remains unknown, and she's shown to have an English husband).
McLeaned: When Josh Charles decided to leave, Will was killed off suddenly in a courtroom shooting.
To lesser extent, Sarah Silverman is a host of Ashley Madison-esque site.
Wallace Shawn's role as Charles Lester is far more sinister than the neurotic characters that he's been known to play.
Michael J. Fox as an unscrupulous lawyer willing to use his disease to manipulate juries. Probably one of the only outright Jerkass characters that Fox has played in his career.
Matthew Perry was also willing to avoid playing it safe by taking on the role of slimeball Mike Kresteva.note Though not for the first time: he’s appeared as a cutthroat weasel before in a guest appearance on Dream On, and even dropped a few F-bombs there!