Marvel announced today at San Diego Comic Con that Cobie Smulders will be reprising her role as Maria Hill for Agents of Shield. She will be appearing in the first episode with other appearances scattered through out the season.
Here's what Joss Whedon had to say:
“I wanted very much to have Cobie in the pilot because as much as anyone else, she IS SHIELD. She’s cool and commanding, and has the dry humor that plays so well with Clark’s. Also, if she’s in it I get to hang out with Cobie.”