It's rare that I write him, but in my opinion, my favorite Cedric moment, even though he's not even in the pairing that I was writing, is Choke On It, the Oliver/Marcus fic I wrote during my 24-hour ficathon. Don't be scared of the O/M, it's brief and insult-ridden, i promise.
The only other thing I've ever written was Other Outlets, some Cedric/Oliver that I seem to have written for no reason at all, other than that I like them both and they both liked Quidditch.
Oops, I lied. There's also One Last Ride, a random drabble for hp100 about Cedric and, you guessed it, Quidditch.