"Oh, man!" - this one is a little tricky as it can be used in several situations. Here are a couple of examples:
It can be used when you're surprised/excited/encouragement -
"Johnny your Dad bought you a new bike"
--- "Oh, man! Really? That's awesome!".
It can be used when in disbelief/disappointment -
"Timmy stole Johnny's new bike"
--- "Oh, man! Are you serious?".