I just went through the GPS evaluation process and got a portable TomTom XXL-550-TM, presently on sale at Crutchfield for $180 plus free shipping. This has a decent sized screen (5"), a mount, plus lifetime traffic updates (via a builtin FM receiver) and lifetime map updates (via USB cable to your PC). It offers a nice feature called "advance lane guidance" that gets you in the correct lane for an approaching turn.
I thought it was a decent feature set at a decent price. The TomTom user interface has been totally revised within the last few months and IMHO they are much easier to use than other brands I examined.