Admiral:
What are the most useful thicknesses of plasticard for modelling/scratchbuilding infantry miniatures, namely Chaos Dwarfs? Are there a few standard choices which you could recommend?
Skink:
Er… I usually go for 1mm thick plasticard. All my warmachine bases are made with it.
tjub:
Guess it depends on what you are going to use if for? 
HPN:
I don’t think you can really go wrong with 1mm. Sure, there could be some uses for thinner and thicker, but a couple of 1mm sheets at home makes me feel “well equipped” for almost any modellistic project.
cornixt:
I never remember what thickness I buy, I just feel it in the store and pick the one that is most appropriate.