Navigon or TomTom, but you gotta pay. Navigon was on sale for $25 last month - not sure now.
Neither of them is as good as Google Nav., but it's the closest you're gonna get.
There are many others out there for free, for $.99, and everything inbetween, but most of them charge monthly for voice guided turn-by turn.
If you're looking for a quick and dirty app that's free and will get the job done, MapQuest is pretty good - but it definately ain't Google Nav lol..
