For soft saturation jobs, PSP mixsaturator.
Harder stuff, CamelPhat and Voxengo Boogex. Boogex works with impulses (it's a guitar cabinet modelling kind of plug in) so you can get plenty of variety with it. Try using delays with that, or even speech samples!
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Also the Korg MS20 fx variation from the Korg Legacy collection has a meaty overdrive, but I haven't found a way to soften it, it's really really heavy. Oh yeah and Fruity's waveshaper too.