While vosotros is the most obvious grammatical difference, there's also another form that's used only in Argentina - the vos form. It conjugates much like the tu form, and for non-native speakers, it is much easier to understand than to reproduce. Sometimes it and the tu form will both be used in the same sentence, confusing things even more.

Example of usage: "¡Vos sos loco!"
   Valentín to Molina in El Beso de la mujer araña

Another difference is visible in pronunciation - Spaniards pronounce "s" sounds that do not come at the end of words as "th" sounds.