The one the always annoys me is the use of "he and I" when "him and me" should be used. "He and I" are the lazy default. As in, "Give some of that cake to he and I."
One grammatical error that's been grating on me in recent times is the use of the word "less" when the word "fewer" is the correct choice.
Many people -- media people, notably -- who substitute the nominative case for the objective do so in an attempt to sound grammatically knowledgeable, I think. They're just not aware of constructions like direct and indirect objects, objects of prepositions (your example), and subjects of infinitive phrases ("We asked him to be our captain").