Rodney

A phone call or voicemail is appropriate; I would drop by as a last resort, if you don't a) get a response from him or 2) get a recommendation from him in the mail by the middle of next week.

If you have to approach him in person, leave one more phone call, expressing your concern that this very important (to you) task won't be done). Then tell him that, in your uncertainty over what's happening, you'll be dropping by if you don't hear from him.

This ploy gives him both notification of your visit and one more chance to respond and head you off. By telling him exactly what your next move is, you've put the ball in his court. If he doesn't want you to show, he has to call. If you do have to show, you've done all the right and polite things to press your case, and he doesn't have the slightest case for getting upset about it. Of course, that doesn't stop some college profs!

Some people are just naturally tardy at writing recommendation letters. I had a college intern working with me last summer, and she asked for weeks in advance of her departure for recommendation letters from us three permanent staffers. I think I'm the only one who got around to giving her one, and even then it was the last minute!