Nav4All, the Java-based voice-guided navigation system that's free (well, until 2008, at least) is now Nokia N95 and 6110-friendly, able to use the built-in GPS. 'Test version' 7.4.1 is the one that'll get loaded up if you use the link below.

To install Nav4All visit www.nav4all.com/install
on your mobile web browser. "

Note that Nav4All isn't the most pretty or intuitive application in the world, but in my initial tests it looks like it's very functional.