Rusty BBQ Grill

http://frugalliving.about.com/od/cleaningtipsandrecipes/qt/Rust_Removers.htm

The above was the first thing I could find and you can use what's in the house.

Dab vinegar on, let it soak, rinse off and dry.

Or, use Borax in place of vinegar and repeat the rest.

Also, when you've gotten rid of the rust, you can protect against it by spraying grill spray or cooking oil. It's like taking care of cast iron. In fact, my grill has cast iron grates and that's what I do.

If it's the outside steel, you might try scrubbing it off with a Chore Boy,a sponge with a non-metallice side that acts like a brillo pad for surfaces you don't want to scratch. If it does scratch, you can always put in some heat resistant enamel paint to protect it in the future. I use a Chore Boy on the dishes and teflon-coated cookware. As for the grates on the grill, being cast iron I use one of those grill brushes with a scraper and metal bristles. But the outside of it, I would use the sponge thing. Then dry completely, then touch-up paint, if necessary.