I thought, on this fine snowy morning*, we could start keeping track of the things.
There's one in Avengers: Initiative #15, with a fairly key role. (He's been mentioned before, by King Mungi.)
There's one in a single panel of Runaways / Young Avengers (Snowbird / a twin / Guardian?).
Those are the two whose appearences I have, but there was at least one more.
Edit:
Both previous mentions came from the thread So what do you think this will do?.
- Le Messor
"Explore until someone yells at you."
- Dr. David L. Hall, HRB Systems
* It snowed at my house this morning for the first time in, what, 8 years? WooHoo!