We bought a Garmin 376c last year and loaded the Bizer Garmin chart and it worked great. I liked the Garmin as it was portable, had really long battery life, and an integrated antenna. There was nothing to mount in the boat (unless you want to). But we chose to leave it portable and use it for day trips.
The 276c was cheaper and the only difference is the XM weather tracker. I don't use that function as it is a subscription service.
I found mine at West marine as an end of season deal, it looks like they are now going for around $600 for the 376c and $450 for the 276c.
The screen is small, but it offers various view options and the portability made this the perfect unit for us.
The Bizer chart was great and easy to load. It shows most of the hard copy information. Here is the link to the Bizer garmin page:
http://www.bizer.com/garmin/index.htm