Though it's Stephen Colbert's debut week on "Late Show," Jimmy Fallon so far has had the most talked-about late night viral video of the week, as he reunited last night with Justin Timberlake for their latest "History of Rap" medley. Enjoy.

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at