Jennifer Aniston Jennifer Aniston

30 Rock
9:31 pm/ET NBC
With Friends like these...Jennifer Aniston continues 30 Rock's rockin' run of great guest stars. (Last week featured Oprah. Next week: Steve Martin.) She plays Claire Harper, who randomly arrives in the Big Apple to visit her gal pals, Liz and Jenna. But Claire isn't so fair. She's quite the scare, actually, a romantic prowler ready to pounce. Before you can say "fatal attraction," she zeroes in on Jack. Meanwhile, new page uniforms depress Kenneth, so Tracy raises his spirits with a surprise involving Night Court cast members Harry Anderson, Markie Post and Charlie Robinson. — Dean Maurer

For full episodes of 30 Rock, visit our Online Video Guide.

ER
10 pm/ET NBC
Anthony Edwards returns to County tonight, giving fans of the long-running show one last glimpse of the beloved Dr. Greene in action, thanks to flashbacks involving the newest ER chief. Apparently, Banfield knows County better than we thought. As she recalls the treatment Greene gave her son years ago, we see that Dr. Greene may be gone, but he's definitely not forgotten. — Rhoda Charles

For clips of ER, visit our Online Video Guide.

Grey's Anatomy
9 pm/ET ABC
It's out with the old (Erica Hahn, gone following last week's dustup with the chief and breakup with Callie) and in with new cardiac surgeon Virginia Dixon (Mary McDonnell), who suffers from Asperger's syndrome. It's an illness characterized by social awkwardness, so it'll be interesting to see how she interacts with the intensely social hot docs. Also signing on is another intern with ties to Meredith: her old friend Sadie (Melissa George). The problem for Sadie tonight is that nobody else is friendly to her. — Paul Droesch

For full episodes of Grey's Anatomy, visit our Online Video Guide.

Smallville
8 pm/ET CW
If only Clark's friends weren't always getting into scrapes! Tonight Brainiac drains Chloe's memories, leaving Davis as the only person she knows and the only person who would tell her that she shouldn't marry Jimmy. Clark, realizing that he needs help to save his best bud, rebuilds his fortress and asks Jor-El to restore Chloe's mind. He is truly a super friend. — Rhoda Charles

For full episodes of Smallville, visit our Online Video Guide.

It's Always Sunny in Philadelphia
10 pm/ET FX
It's Extreme Makeover: Sunny Philly Edition, but don't expect Ty Pennington and, more important, don't expect to feel warm and fuzzy as the gang decide to do a good deed to a deserving needy family. What did those poor folks do to deserve this? You shouldn't be surprised to learn that our not-so-good Samaritans are in it only for themselves. — Paul Droesch

For full episodes of It's Always Sunny in Philadelphia, visit our Online Video Guide.