Ouch. I think I might have done it once or twice, but was able to see the end and grabbed it.
Start with an inspection mirror (like the dentists use) to see if you can put eyes on it. Then I would go with a small telescoping magnet, preferably one with an indexable/jointed head and start gingerly fishing around for it. Hopefully it's still laying against the cam.
Did you hear it tap several times on the way down and maybe hit the oil pan?