Offmaps will let you download map data in advance and use it offline. I used it on my last trip to Beijing (where I knew I wouldn't have Wifi access). Just highlighted the area I wanted in advance before I left the US and had it download the maps. Took a little bit to download them over Wifi, but once I had all the data stored I had everything I needed. I think I was also able to download POI's off of Wikipedia as well and store those.
The second I got off of the plane in Beijing, I had map data as the taxi took me from the airport to my hotel ... and every business I visited while I was there.