While being a "series regular" doesn't guarantee anything on The Walking Dead, it does come with a pay bump and a certain amount of prestige. So in addition to David Morrissey, there are several other very happy actors returning for season four.
Returning to The Walking Dead next season as full-fledged cast members (as opposed to recurring cast members) are Chad Coleman (Tyreese), Sonequa Martin-Green (Sasha), and Emily Kinney (Beth). While Coleman and Martin-Green only joined the cast this past season, it is about time Kinney got the promotion: she has been on the show since season two, and her father and sister (Scott Wilson and Lauren Cohan, who play Herschel and Maggie) were upgraded at the start of season three.
Also returning for season four is Melissa Ponzio. She plays Karen, the lone survivor of the Governor's psychopathic bloodbath in the third season finale. Ponzio will come on as a recurring guest star.
The Walking Dead returns for its fourth season this October.