I'd been told that best idea for currency exchange when arriving is to use the banks at Narita, so I did. Wish I had waited. My Japanese buddy (who I saw on Day 2) told me "best kept secret" are "Discount Ticket Shops" (Daikoku-yu) -- always an orange colored sign. Most but not all of them have a money exchange for USD, GBP, Euro, Aus-NZ, PRC, ROK. We checked the rates at several and all were better than Narita, as well as the banks in town. Rates vary slightly among them, best we found was in the plaza adjacent to Yurakucho Station (roughly between Ginza and Hibaya Metro stations). Wish I knew about them before I did big exchange at Narita!