Possible Clues:

• Slangy OK
• Kelly Clarkson "My December" song
• First or second word of Karen O's band name
• Fist-pumper's cry
• 'Couldn't agree more'
• Single from Usher's 'Confessions'
• Positive (or sceptical) exclamation
• One-third of a Beatles refrain
• 'Good going!'
• 'I guess that's true'