flyinH, the ML500 comes with navigation and I really like it, personally. It's very easy to use and it does the job very well. coyotefreek is probably right, that out of all the different nav systems out there, it is not one of the better ones, but I have absolutely no complaints about it. The salesman showed me how to use it when we first picked it up and I have no problems operating it at all and no complaints, either.
coyotefreek, one thing you should know is that the navigation system in the ML is different from the other Mercedes models. The ML's navigation system is called MCS or MVS or some crap like that. But in my parents' 04 S500's, their cars feature the COMAND Center, which is very different in terms of layout. Personally, I think both systems do their job and work just fine...my impression with navigation is that once you learn how to use it, they're all the same shit.
But if I had to pick a personal favorite, it would definitely be the Lexus navigation system (our RX300 has it). I like it because the touch-screen makes it very easy to enter addresses (just touch the letter, rather than working with some silly little joystick). Also, when there are turns coming up ahead, it splits the screen, one half of the screen shows a direct over-head view of the car from far away, and the other half shows a zoomed-in image that is easier to read and has a meter on the right telling you your distance from the turn.
There is one thing I HATE about Japanese navigation systems....why don't they let you enter the f-ing address while you're moving !!! It's sooo frustrating !! The ML500 and the S500's just warn you when you wanna put the destination in while moving, but then you click OK and you can just enter it. The RX300 and my Infiniti completely block my ass out if I try to input a destination while moving !!
Oh and if you want, I can take video with my DigiCam of how to input a destination with the ML500's navigation system...it's really not that bad, and once the destination is put in, the voice guide and map are flawless!