Frasier

From the moment Kelsey Grammer's Frasier opens the door to David Hyde Pierce's Niles in the first episode it was clear this was going to be good. Yet the part of Niles wasn't even meant to be in the show when it was first conceived as a spin off from its long running predecessor Cheers. The role of Niles was created when the producers saw a picture of David Hyde Pierce, and footage of his role as Theodore in "The Powers That Be", a sitcom that ran for 2 seasons in 1992 and 1993 and starred John Forsythe as a hapless senator, Hyde-Pierce was his suicidal son-in-law.
John Mahoney (Martin Crane) would often give advice to Jane Leeves (Daphne Moon) on her Mancunian accent. Mahoney's family being from Manchester, he moved to the US as a young adult and became a citizen after a stint in the US army. Leeves was born in Essex and moved to the US after working in British TV notably as one of Benny Hill's "Hill's Angels" in The Benny Hill Show.
The final human part of the regular cast was Peri Gilpin as Roz Doyle, who was born in Waco, Texas and grew up in Dallas.
Eddie the Jack Russell was often to be seen stealing the show, played originally by Moose and then later by his son Enzo.
Here's some Frasier outtakes