Gauger is pretty cool for lots of experimental sounds.
Some old school ensembles that have been around since V3 that are cool are Plasma which is a cool granular sampler thing which has a sample start and speed parameter that has a knob to be automated and is better than Kontakt imo for certain sample playback and Weedwacker (which might be the weedbacker one already mentioned although mods to ensembles do exist and get named similar) which makes crazy noise but is an 'instrument' that you can play.
I like messing with that one as well... but I haven't completed any projects with that ensemble in it.
i use it in many tracks
you can get some monster evolving sounds with it, i always do a midi line and resample it looping it 2000 times and changing a lot of paramenters on Oki c that i setted on my controller