Outdated, For historical interest:

You can use the free Tiger maps for US.

Quick howto :

The conversion script converts tiger to osm v4 (where navit uses osm v5) but hopefully there is a script which can convert osm v4 to osm v5...

So the procedure should be something like :

Get your datas from tiger. You can get the tiger to osm tools here : http://sr71.net/~dave/osm/tiger/

tiger-to-osm

Now convert the resulting datas to osm v5 (you can get the tool here : http://trac.openstreetmap.org/browser/applications/utils/conv05 )

./04to05.pl mymap.osm

Now, convert the datas to navit binfile :

./osm2navit mymap.bin < mymap.osm

US/Tiger maps