Last season, “Heroes” became a surprise hit for NBC, especially so since fantasy and science fiction have always been a hard sell for the networks.

So now such programs are all the rage on the broadcast channels, as executives hope to find another “Heroes.” That’s especially true on NBC, where two new such programs debut tonight bookending “Heroes” itself.

Up first at 8 is the deceptively simply named “Chuck.” This rookie show is also an example of a popular sub-genre, Geek Chic, sparked by the exuberant Hiro of “Heroes.” (Another lesser example is “The Big Bang Theory.” More on this later.)

The titular character of “Chuck” is Chuck Bartowski (played by Zachary Levi), a Stanford dropout who heads up the computer-loving Nerd Herd at Buy More. Chuck is enjoying his normal slacker lifestyle, much to the chagrin of his older sister, Ellie (Sarah Lancaster).

Chuck’s life changes when his hated former roommate at Stanford, now a spy on the run, sends him an e-mail containing all the top secrets of the U.S. intelligence community, and this information is downloaded into Chuck’s brain. (How? I don’t know. “Chuck” takes a healthy suspension of disbelief.)

This knowledge makes Chuck a target, so working to keep him safe are a hot blond CIA agent (Yvonne Strahovski) and a hardcore NSA agent (Adam Baldwin, “Firefly”), both of whom take jobs at the mall to stay close to Chuck. Now Chuck must find a way to live as normal a life as possible while working as a reluctant asset for U.S. intelligence agencies.

“Chuck” is a lighthearted action romp, a welcome change of pace for those wanting a break from dancing celebrities, admittedly well-crafted sitcoms on CBS and the CW or the continually labyrinthine “Prison Break.”

Following “Heroes” is “Journeyman,” a “Quantum Leap” for the new millennium.

The “Journeyman” is San Francisco reporter Dan Vasser (Kevin McKidd, “Rome”), who finds himself traveling back in time to fix people’s lives. The problem is that he has no idea when and why he’s time-shifting.

His dead fiancee, Livia (Moon Bloodgood), keeps popping up when he goes back, which isn’t helping things in his troubled marriage or at his newspaper (I’m guessing the unexplained absences don’t either).

“Journeyman” is an intriguing twist on an old concept, for those who seek something different than forensics done by pretty people in a warm place or women lusting after the hunk du jour. However, it may require too much thought at 10 p.m. for many viewers.

Last up, barely worthy of mention, is CBS’ “The Big Bang Theory” at 8:30 p.m. In it, two socially inept physics geniuses chase after the pretty bubble-headed blonde living across the hall. That seems to be the entire premise of this show by Chuck Lorre, which makes his double entrendre-packed “Two and a Half Men” seem positively nuanced in comparison.