I promised to post some example from tomtom gui so here it goes
http://aijaa.com/v.php?i=000948347385.jpg

1. Animated compass needle showing your current direction in degrees.

2. Graphical sign for next turn & distance to turn

3. The number or name of the road your are turning

4. from top left. Calculated time for routed trip, current time, speed (sometimes in format xx/80 to show limit), total distance to end. On far right are the bars for satellite coverage.

5. Zoom buttons (Far away from each other to minimize occurrence of miss taps of wrong button)

Of course you can just turn on/ off most of these from settings. IMO e.g. white text on blue background really really jumps out from screen. On N900 maybe the best compromise would be to use right or left edge of screen with column of ~200px