Chords over riffs ??

So I've been a good boy and am learning the modes, doing alot with intervals, and chords (like I should of years ago). So today I wrote a little riff (C maj) but just cant figure out the chords to go behind it. Is there a method to the madness.

Because of learning modes and intervals, I have been writing alot of little songs with my guitar port and Riffworks, just to help me with what I have been learning but, I am really stuck when it comes to this little riff based song. I dont want it to sound like a happy childrens song.

I can post the little song if needed but really want to know if anyone has a formula for disecting riffs and figuring out the correct chords to play.

Thanks in advance.

You could try: A minor, F major, G major,E major, D major they usually work with C maj

The short answer is: Harmonizing your scales or modes.
There was a thread that can help you understand, what chords to play with an specific scale or mode for that matter.
http://www.guitartricks.com/forum/showthread.php?t=14324
good luck.

Thank you for your replies! :D