I have the Nuvi 350, looking to get a slicker package, I may get a 600 or 700 or 800 series.

Look at any of the Garmins on Amazon and scroll to the bottom - they have a really good chart that shows which models have which options. Very helpful when trying to see what to get without buying more than you need. Plus it has great real reviews from people who have used them.

The single piece of advice I give everyone is to get one with Spoken Street Names - like "Turn right in 300 feet on Oak street", not just "Turn in 300 feet" - makes a world of difference.
Good luck!