I am looking at buying an 06 gs430 or an 07 gs430 with nav, what are other options that I should be aware of?

 

Mark Levinson audio, for one. the nav seems to have been upgraded in the 07. you may have no lock-out for the vsc...
Great choice on the car, btw.
check this out or the diffs in model years:
http://en.wikipedia.org/wiki/Lexus_GS_430

 

ML, Rear Shade, Parking Sensors, Adaptive Cruise. Those are the major options that you'll find. Adaptive cruise is more rare. If you find one with ML, they *typically* have the rear shade and parking sensors too. I'm missing something, I know it.

Oh...07 GS430's are very rare. Good luck finding one. There are a ton of 06's. In 07, they are mostly GS350's.

 

best thing i would say is the ML system. a lot of dealers say premium sound which fools people. easiest way to tell if the car has ML is to look at the center console on the bottom right, just above the ashtray, it should say Mark Levinson. ML also gives you the option to play dvds.