You guys might know these but I'm sure not everyone will know all of these so here they are. Have fun!
A REALLY frightening scream variation:
Play two pinch harmonics (easiest on an upstroke; this makes it easier not to mute the first note allowing them to sound simultaneously) and bend one of them up to the higher note and back down. Try fretting a D at the 3rd fret on the B string and playing harmonics on this and the open string. Bend the note up to an E and back down. You get this really eerie ringing sound as the waves go out of phase and come back in.
Behind the nut bends.
On a non-locking nutted guitar you can bend a note by pushing down behind the nut. This can be combined with harmonics to make a sound like the trick above.
Tiger Purr
A floydd rose can make a nice buzzing kind of "Tiger Purr" sound, all you do is pull the whammy bar up and drop it back down fast. It buzzes its way back to equillibrium. Pettrucci's a big fan of this one.
Violining (AKA Volume swells)
Pluck a string with the volume down and, curling your little finger round the volume pot, gradually swell the volume. This cuts off the "attack" of the note which is characterised by high harmonics. This way you get a smooth kind of sound. Sounds great with delay. Combine this with Auto wah and you get a combined Wah and volume swell effect.
Harmonic Triad
You can get a major triad from natural harmonics really easily: play 5th fret, then 4th, then 3rd.
Wobbly sound.
Flick between your pickups rapidly, you get this kind of weird dis-continuous wah type sound. I've only heard one other guitarist do it: Mike Mcready (Pearl Jam) on the song "garden", it sounds great. You can optimise the effect by making your neck pickup really bassy and your bridge pickup very trebly.
If I couldn't laugh at myself how could I laugh at someone less ridiculous?