Redbox, the company that sets up DVD rental machines at supermarkets, drugstores, and convenience stores, has quietly been adding their machines at airports. For the same $1 per day rental fee, travelers can pick up a movie in one airport, watch the movie on the plane, and return the disc at any Redbox, at the airport or not.

Nashville, Milwaukee, and Grand Rapids have had them already for several months. Boston and Cincinnati were just added. Some airports have them before security; some have them both before and after security.

It’s a brilliant idea. Cheap last-minute inflight entertainment for those bringing a laptop or a portable DVD player. (Of course, you’ll need a device that plays a DVD (most netbooks don’t have an optical drive anymore) and if you plan ahead you might have something else at the ready.) And make sure your batteries are fully charged.

The company is also making deals with in-airport concessions. For example, at Cincinnati’s airport, buying a popcorn and soda combo at a vendor called Buckeyes & Bluegrass yields you a free DVD rental code. Expect more tie-ins like this.

My biggest beef with Redbox (which I’ve only accessed at my supermarket, not while traveling) has been the selection. Yes, they have some recent films, but there is too much straight-to-DVD junk in their inventory. I hope their airport locations have a more desirable selection, and remain well-stocked.