We've had great luck with the Garmin 76... but replaced it with the Garmin Colorado 400C and there is no going back! Full color and all the charts already unlocked. We had a couple little quirks with the 400 to start but got them figured out and haven't had any trouble since. Biggest one is to turn the backlight fully off (no need for it during the day) or battery will die really fast, and to use lithium ion batteries.
It's worth buying it at West Marine since they have it at $3-$350 and offer great coverage on them (especially if you become friends with the manager).
You can buy a cheaper one but the fees to unlock the charts adds up fast.
We use a foretrex on each side of our boom, never had the battery die on the water... use more for speed and vmg than navigation though.

Side note.... went to turn on the 76 the other day and it doesn't work! The springs inside the battery case have rusted a little bit. Anyone know where I can send it for service?