My favorite is an Audio Technica 419 which is technically a horn mike, but when you run it through a tube pre-amp (like an ART MP, which also delivers the phantom power the mic needs) it is smooth and sweet.

The only problem with those clip mikes is if the fiddler is a heavy breather. Then you need to tape the portion of the mic with one small piece of duct tape that faces the fiddler and leave open the portion that faces the fiddle bridge, then cover with the small foam windscreen that comes with the mike.

Clip the mic to the chin piece and experiment with the placement of the mic head. (Aiming it at the left F hole on the fiddle is a good start). Remember that you could get feedback if you take the fiddle down and aim the mic portion at a monitor. Good Luck!