I am using the Stanford POS tagger to parse questions. It is one of the best POS taggers available in my experience, but a simple question like "When did Nixon die?" is incorrectly annotated as
When_WRB did_VBD Nixon_NNP die_NN
As stated in the comments, "The Stanford POS tagger currently gets this correct."
Lol... I'll take the bounty if he doesn't want it.