Tina Fey is really trying to bolster 30 Rock's mediocre ratings with a slew of fancy guest stars. First there was Oprah, and tonight, Jennifer Aniston will make her appearance as Claire Harper, the psychotic former roommate of Fey's Liz Lemon. Click on Aniston's mug for a clip of her singing a Marilyn-inspired version of "Happy Birthday" to Alec Baldwin's Jack Donaghy. [Mirror]