There is a real deficit of mapping software for the MAC out there right now.
http://www.routebuddy.com/routebuddy/index.html
is one program but I've not used it beyond the demo. Seems mostly capable but the company isn't very good at disclosing how old the map data is or the frequency of updates.
Good hunting, let me know if you find anything of use asI'd also like something that doesn't require an internet connection to use. (like google maps)
Google maps works OK when I'm on-line but in the Pacific NW you aren't always close to a cell tower