Oh god, too many things to all write down. But some I dare to do IRL:

"*Koolaid Guy voice* OOOOOOOH YEAH! *thumbs up*"
"Ooooh snap"
"Oh. Dear. GOD."
"*Napoleon Dynamite Voice* GOSH! ;______;"

I have a bit of a catchphrase with everyone offline, though they're not so much catchphrases but greeting inside jokes like "A 1,000 YEARS OF DEATH" and "Brown/Black/White/Scottish Man/Woman Lies!" and "You must be smoking weed behind your ears, boy!" among other things.

Not to mention saying everything is awesomesauce, coolsauce, burnsauce, sucksauce, rofflesauce and yaysauce. I even do that IRL a bit, but I do it overboard online. But then again, like I said, more inside joke greetings.