Check out highlights from The Big Bang Theory Season 6 in this video. It debuted at Comic-Con 2013.
Added:
The Big Bang Theory Season 6 gets underway on September 27. Check out the first promo for the premiere now.
Added:

The Big Bang Theory Season 6 Quotes

Raj: Okay, here's another one: if a zombie bites a vampire, and the vampire bites a human, does the human become a vampire or a zombie? Or, a zompire?

Amy: Soon my upper lip will be the same fake blonde as my beautiful best friend.
Penny: Hey, this is my natural hair color - Now.