is there a map app like google maps that will work on an offline iphone? a mac os x app will do, too.

There are several apps that do this. My favorite now is http://www.mapswithme.com/. It's unusual in caching vector data, so you can draw very detailed maps with relatively little storage. It's also free, although the paid version has some nice features like street name search. There's also an older generation of apps like http://www.offmaps.com/ that cache raster OpenStreetMap map images. The maps are prettier but they take a lot more space and you can't zoom in as far. I'd start with Maps With me and see how you like it. It's particularly good for walking around European towns. Neither of those apps will do driving directions; only show you maps. If you need offline directions it gets a lot more expensive, you need to buy TomTom or Navigon or the like for about $50. These apps are great, full replacements for standalone GPS navigation units. But they are expensive. One other stopgap that works; you can get directions while on WiFi in the iOS maps app, then use those while offline. This seems to work pretty well, but I don't know if the app is designed to really work this way or it just kinda does. iOS 6 is widely rumoured to have a new maps app. My fingers are crossed it has offline support.

There are a handful of OpenStreetMaps-based offline maps apps. OSM's quality is variable; in some regions it's quite good, in others not very good, so you might want to evaluate it against another map before deciding to use it.

There's always http://www.copilotlive.com/us/ - I have the Android version and like it.

I also use and like http://ulmon.com/ on my iPhone and iPad. I tried a bunch of similar apps and it was the only one I could find which consistently got the job done.

I use http://news.motionx.com/category/motionx-gps/ when I travel. You can download maps ahead of time, by region or by the route you're going to travel. It is quite fully featured. Downloading maps is free; only the initial app download costs you (and I think there is a limited free version), so it is worth a shot to see if you like it.

If you want walking and transit directions, get mtrip. I'm I'm London right now with a similar situation and it's the best I've found. I've tried most of the above (and will try the others). Mtrip isn't free, but it's a small price to pay to be so much less annoyed... :)

I also use CityMaps2Go by http://ulmon.com/ on my iPod Touch. .. but the maps are a bit ugly compared to google and its just not as good with customizing the maps as googlemaps is with its Layers and different Icons, and drawing lines and shadings. I have lots of Google My Maps and I wish there was a way to transfer these to my iPod touch. but I haven't worked out any method yet.

Here's details on http://www.apple.com/ios/ios6/maps/. It doesn't look like they did anything offline. http://www.skobbler.co.uk/ ($3 in US) is another offline vector map viewer for iOS 6. On a quick test it's better than MapsWithMe. I'm not wild about the rendering, but the app is very fast and includes some basic offline routing. Address search is pretty limited, but it has a handy database of points of interest: bars, hotels, restaurants, etc. Also walking vs. driving directions.

City maps 2 go is fantastic. I'm on vacation now with no dataplan and downloaded the maps I needed before leaving. The app even has location finding (and a whole built-in list of businesses, transit, etc) so you can figure out how to get yourself from place to place with ease. Between that and using google maps when I have wifi if I need anything more, I haven't had any of the way finding trouble I did last time I was in an unfamiliar place (or data charges!).