If you want a truly fine personal GPS, try the Garmin GPSmap 76CSx, it is top of the line in every way... But be forewarned that it is useless (other than to tell you your lat/lon, of course) without buying map CD/DVD[s].
If you want to use it for boating, you'll need the BlueChart CD[s] for the area[s] you transit. The BlueChart Americas CD is like $150 at West Marine, it's a few bucks cheaper on the Garmin website, but after shipping the difference is negligible -- and being able to walk out of the store with it, has value.
The license that comes with it gives you coverage from Guatemala to half-way up the coast of Oregon -- but the area you get is up to your selection. If I thought it more likely to find myself sailing further north in Puget Sound, or [way] further east in Nantucket Sound I could've selected those regions instead. All it takes to "unlock" other regions is to send more money to Garmin, which you can do over the wire.
If you want to use your GPS for driving too (which is infinitely easier and more convenient than using, say, a Thomas Bros map book) you will also need the City Navigator North America DVD, for which you can expect to pay $100-$150
Make no mistake, I love Garmin's products, they are first rate! Also, their map software is far and away the best in the industry; their licensing fees do not strike me as unreasonable.
The only thing that put me off was that my 3 year old Garmin eTrex Legend GPS shipped with a reasonably workable built-in map set, it had accurate shoreline and prominent aids to navigation, as well as highway and thoroughfare street detail built into it -- you could actually use it out of the box, it even detailed some marinas.
The shoreline map built into the new one is an approximation at best, and excludes man-made features of land that pre-date the 1950's. It was a bit of a shock to find that I needed to go out and buy something else before I could use it at all -- and the fact that they do not offer download as a method of delivery for the maps didn't help any either. (You can unlock additional regions online, but you must wait for the mail or find it in a store to initially buy it.)
Otoh, having bought the maps I need, I wouldn't change my decision to buy this particular model (or brand, for that matter) for even a second. I am very pleased with its functionality as well as its user interface and the readability of its 256 color screen. I would highly recommend it to anyone shopping the high end for this sort of device.
I bought the device itself from www.gpsonsale.com for $345 delivered. The total cost, including BlueChart and City Navigator maps was about $620.
Note: some Garmin GPS units, such as the dash-mount StreetPilot series, do include extensive built-in or bundled map data.