First--check to make sure the listing is actually approved--and if so, do a "find businesses" search for it on maps.google.com. If the listing still doesn't appear, head over to your Local Business Center Account and click "edit" next to the rogue business listing. Then, without changing any of the info, hit "finish." There's no need for re-verification, and the listing should appear within 24 hours.
Read the whole story at Understanding Google Maps & Local Search »