What are some fun/special pieces of equipment to use with a Canon 5D Mark II?

My school’s film club just bought a Canon 5D and we’re looking into using the rest of our yearly budget on some other video equipment (not for still photography purposes). What would you buy extra (besides lenses) that would be fun, interesting, and/or useful to have?

We have a budget of $1,500 right now, and next year we will have $3,000 extra.