I didn't have factory NAV either. I had a local shop install mine. They did a Lexus double DIN kit and custom made the faceplate from a Lexus ES and epoxy/fibered it and painted the center to match. It was intensive but worth it in the end. My new setup has USB, ipad controls, BT, large screen that allows navigation of mp3, ipad playlist, phone controls, etc. It doesn't have NAV (they make one) but I use my ipad with motionX and google maps for NAV since it pauses music/pandora while the NAV talks. It is a sleek step above the GROM on OEM stereo (I thought the GROM was okay, but it wasn't "perfect").
Oh, and the JL Audio and high end alpine speakers/amp, etc makes it 1000% better than any stereo you could muster with OEM components.
Happy to share pics if you need an idea of the final look.