McClintock followed up with a 1999 guest role on "Felicity" (The WB) playing the homosexual older brother of Noel, the titular college student's love interest and resident advisor. Later that year he was featured in an episode of the same network's Manhattan-set teen sitcom "Zoe, Duncan, Jack and Jane" as an incompetent waiter who wins the help and, unwittingly, the heart of zany young Zoe. While these efforts made his face familiar to a larger audience, McClintock's real breakthrough came with a regular featured role on the NBC sitcom "Stark Raving Mad" (1999-2000), co-starring as the offbeat writing assistant to a successful but strange horror novelist (Tony Shalhoub). Neil Patrick Harris rounded out the cast as the harried editor, and the draw of both he and Shalhoub as former stars of popular series (along with a cushy pre-"ER" time slot) aided in gaining the show a larger audience and a longer run than "Holding the Baby" managed to secure.

On the big screen, McClintock could be seen in several small scale independent features before appearing in Lawrence Kasdan's 1999 release "Mumford.” He later landed a starring role in the romantic comedy "Moving August" (2000), playing a young photographer moving out of his apartment who falls in love with the woman moving in. After a brief appearance in Steven Soderbergh’s pretentious return to indie filmmaking, “Full Frontal” (2002), McClintock was in an episode of the short-lived sitcom “The Pitts” (Fox, 2002-2003), then played one of many suitors vying for the affections of an up-and-coming book editor (Charisma Carpenter) in “See Jane Date” (ABC Family, 2003). He had his first regular series role in “A.U.S.A.” (NBC, 2002-2003), playing the wise, but fun-loving roommate of a young lawyer (Scott Foley) starting his career as a U.S. prosecutor in Manhattan. McClintock had a more substantial part in “Picking Up and Dropping Off” (ABC Family, 2003), a romantic comedy about two single parents (Scott Wolf and Amanda Detmer) finding solace in one another after being divorced from their spouses, then appeared in episodes of “Married to the Kellys” (ABC, 2003-2004) and “Less Than Perfect” (ABC, 2002- ).

Appearances on “Monk” (USA, 2001- ) and “House” (Fox, 2004- ) were followed by meatier roles in “Three Wise Guys” (USA, 2005) as a cynical ladies’ man and “Confessions of an American Bride” (Lifetime, 2005) as the old flame of a doubting bride-to-be (Shannon Elizabeth). McClintock returned to regular series work with “Crumbs” (ABC, 2005- ), playing the estranged skirt-chasing brother of a failed Hollywood writer (Fred Savage)—who is also a closeted gay—returned home to help run the family’s restaurant. Both must contend with their womanizing father (William Devane) and neurotic mother (Jane Curtain) who spent time in an insane asylum after going berserk when she discovered an extramarital affair. “Crumbs” was ordered to series midseason in 2006 and faired well enough in the ratings to get a network order of 12 episodes.