I have been using this for years. I also gave one to my dad 2 years ago. The carts are great and up to date. Shows underwater obstuctions and alot of other info. easy to see in the boat and very accurate.
http://www.lowrance.com/Products/Outdoors/iFINDER-H2O/

I didnt read everyone elses responses but i have a Colorado 400i, it has all the waterways on it with depth markers and bouys...i would recomend it and I also just loaded topo maps and use it on my mountain bike.

Wife bought me a new Garmin 640 at the Miami Boat show this year....... I will be installing it in a few weeks. Been tinkering with it and it seems great..... touch screen, built in maps, can use it in the car or the boat, etc, etc....... when I add the g2 vision card you get overhead pics and auto guidance..... all for $800(may have been a boat show special?)......... not to bad in my opinion.....

I am looking at the Garmin 441 and 541 for 599 and 799. I have not seen the 640.

have two old handhelds. garmin 111+, and magellan color. LapseofReason is right no trips to the bahamas with the garmin. the magellan a little better. use the magellan for the truck, boat, and snowmobile. works fine for marking fishing spots, dock, ect. good mph, and heading to get home. will keep you out of fishing in canada waters too, and that's a big one. they take boat and all. Asking anything more of a handheld is pushing it. If you don't need to go blue water and you know the area then they're great. Will take the beating of the boat and will take a shower now and then, better than the ones for the car.

garmin gpsmap76 (i think)...can pick one up for less than 300, with software....not a lot of frills, buy it will get you there and back just as well a big$$ one...you just need a bit of time plotting the courses on the old pc...and uploading them, but it's easy to do...

Got a Garmin 431s. Haven't put it through its paces yet but seems to be pretty useful and not on the expensive side.

Got me a Garmin 478 and I am really happy with it.

Here is the link....... I didn't realize it has an MSRP of $1199..... I guess my wife got a great deal at the boat show.......

https://buy.garmin.com/shop/shop.do?pID=14898