i am in the market for a new sonar unit this winter and am looking for some feedback.I have 2 garmin 240's and am looking to replace the one on my trolling motor.I was thinking about sidescan but way too expensive. I am willing to spend up to around $600....what are your suggestions.......thanks

Whatever you decide, wait for a sale. BassPro and Cabela's always are having sales. Also look at Cabela's Bargain Cave, and the fishing flea market on this sight. 

Humminbird 788.  640x640 color screen, dual beam sonar, gps with mapping.  $499 at Cabelas.

HDS 5 and then you have the option to add side scan in the future.  Also Lowrance is coming out with a new unit in the next couple months that has down scan only that looks pretty sweet.  I believe that will be in your price range.

i have a stupid question....do the sonars with gps need lake software or do they work like gps for cars.I always assumed you needed the lake maps loaded in..

They can't operate like auto GPS units since there are no roads to travel or cites to go to by water (most places anyway).

Lake mapping is not a requirement for function but a nice addition. The mapping softwere has no function regarding the GPS, it is just overlayed on the screen as a reference. Basically you cannot pick a location to go to and the unit will guide you around obsticles whether it is a point or island, etc.

The main thing about the GPS units is the abitity to save locations (waypoints) that allow you to return to them from anywhere in the world.

The plotter (track plotter) units will draw a line on the display as you move about and you can follow that line back to its beginning. That line (track) can be saved also.

The plotter units will put a straight line on the screen between your starting position and any saved waypoint that you chose to go to that will help you get there.

i am in the market for a new sonar unit this winter and am looking for some feedback.I have 2 garmin 240's and am looking to replace the one on my trolling motor.I was thinking about sidescan but way too expensive. I am willing to spend up to around $600....what are your suggestions.......thanks

The side imaging is the way of the future.  Whether you get it now or not at least get a unit to which it can be added later so you won't be sorry.