I wish someone would make a light with a snap on bayonet lug mount.  Not a rail adapter that bolts onto the lug, but a light that easily snaps on and off.  It's impossible to put a bayonet on my 16" barrel anyway, so it would be nice to use the lug for something other than just looking cool.  Also, even on rifles where you can mount a bayonet correctly, I read that if you ever try to use one on an AR15/M16 you are going to tweak the crap out of the front sight base anyhow and throw your sight alignment off.  Why not use the lug for something practical?

Either that, or a death-ray laser that would vaporize all in my path.  That would be cool too.

Quoted: I read that if you ever try to use one on an AR15/M16 you are going to tweak the crap out of the front sight base

Only if you own an Olympic Arms rifle.