From Heather Graham's burgundy sequin dress to Rihanna's bright street style—these are the stars that looked the chicest this week!

News: Celebs Teching Out: See What Your Fave Stars Can't Live Without

Watch: Blake Lively Talks Mother's Day Memories

Photos: The OK! Editors Reveal Their Dream Celebrity Gym Buddies

Who do you think was best dressed this week? Sound off in the comments below or on Twitter @OKMagazine!