look at these web sites.
http://www.mda-vst.com/
mda-vst has a series of AU you can use on your voice.
Detune is nice. Detune - Simple up/down pitch shifting thickener
Leslie is nice. Leslie - Rotary speaker simulator
I use them alone or in combination. Try their different presets or make your own extremes.
Forget about the Talkbox AU. It doesnt seem to work in GB but might in logic.
KTGranulator is a free delay line granulator.
http://www.koen.smartelectronix.com/KTGranulator/
It has many presets. Use your mic and talk or sing into each preset to see what you like. It comes with 40 presets.
Presets 6&7 will give you a metallic sound called metallic 01 & 02.
Preset 16 is called "Android". Try them all you never know. Try combining them with "Detune" or "Leslie"!
Monstachorus is fun. Try the presets or experiment with new ones.
http://www.macmusic.org/software/view.php/lang/en/id/3098/
These are just a few examples. Best thing to do if your looking for unusual ways to change your voice is to try them in every AU you can get a hold of. You just never know what you'll come up with.
also try the tremolo and phaser that come with GB, or even the drum and guitar effects. I like to use guitar effects for distorted voice effects.