We have 4 navigation applications available for Nokia Internet Tablets, but at the same time none of them are complete in nature.

MaemoMapper is a mature and stable application - But Map files are too big to download and importantly, it needs internet connection during travel to do routing/rerouting.

Wayfinder - Involves $130/- for 3 year period. One time investment is OK, but I don't like recurring exp.

RoadMap is a good one, it uses vector maps but so far Routing/Rerouting engine is not available yet.

Finally Navit, similar to RoadMap, it uses Openstreet maps, not fully functional. But as per the developer Navit can do routing/rerouting but so far it is not working. It would be great if he looks into the issue and makes routing/rerouting works.