Strega also (rather unkindly) took to calling Spike "Spicule", apparently a dig at his Badass Decay.
Lorne is nicknamed "Cary" (Cary Okie. Geddit?) for no particular reason other than it sounded better than The Host.
She got through "Dad" by giving the yet-unnamed Connor various names including Cousin Oliver, Godzookie, Pebbles, Little Ricky, Mearth, Robin T. Frog, Albert Ingalls..
Genius Bonus: Izzy, a Devil in business attire. Throwaway gag right? D&D players delineate between Demons, who are Chaotic Evil in alignment, and Devils who are Lawful Evil. Hence, a devil working at a law firm.
Although many would recognise him more for his voice (as mentioned below) Simon Templeman as Matthias Pavayne would also be recognisable to viewers of Charmed, in which he played the Angel of Death in three episodes. He also appeared as Lord Nor in two episodes of Lois and Clark.
The gym manager in "Judgement" is played by actor/stuntman Keith Campbell, best known for playing the alien perp who leaps off the building in Men in Black.
John Kapelos, the hotel manager in "Are You Now Or Have You Ever Been", formerly played Donald Schanke, Nicholas Knight's partner for two seasons on Forever Knight. Possibly as part of an in-joke, there is polka music playing in the hotel in one scene: Schanke was a big fan of polka music in FK.
Joss Whedon wanted Anthony Head to make a guest appearance as Giles in "A Hole in the World", but it would've been to pricey for him to fly from England to Los Angeles for filming. Nicholas Brendon offered to join the cast as Xander during season 5, but Joss declined as Xander didn't have enough of a connection with Angel for him to fit in. Because of this, Xander and Giles are the only main characters from the first three seasons of Buffy who do not appear on Angel.
Jim Profit from Profit was going to be a Wolfram and Hart employee, but rights issues concerning the character and conflicts with Adrian Pasdar's schedule prevented it from happening.
The LA office of Wolfram & Hart was later used as the main part of the LA Dollhouse in that Joss Whedon show.