anything garmin. buy the nicest mapping unit you are willing to spend $$ on. Sounds like the software (lake mapping) is the key thing for you. Shop for that first and ensure it iis Garmin compatible or else buy another brand for which the software will work.
I'm sold on an I pad. Best gps I've seen yet. Plus it does a ton of other stuff. As far as lake mapping chips...not sure. You'd have to see if there is an ap for that available.
The Garmin Map 60Csx is on sale for $200 at gpscity.com right now. Good unit for the price, although it is probably being discontinued with the 62's out now.