You can find the unit I use on this thread,http://www.hobiecat.com/community/viewtopic.php?f=71&t=26131
The reason I bought it was simply cost effectiveness....
You get literally everything in one package for under $200.
There is a color version for around $400...
An added bonus is that this unit has the same footprint as the Hobie recommended unit and fits the RAM mount they provide.
There are plenty of other units with much more precise maps and displays but for a kayak this unit is fantastic.
I have found that I use the simple data screen, direction, depth, water temp, compass and speed, WAY more than the GPS. The GPS on this unit is very nice and is great for marking way points.
One HUGE reason I opted for this unit is the mounting stand. The mounting stand allows precise angular positioning and super quick and easy removal. This allowed me to purchase another sounding head and cable (approximately $80) and another mounting stand (approximately $20) to mount on my Adventure. So now I can simply take my battery box and Depth sounder/GPS unit and use it on either boat I choose to use.... and I built the battery box, installed the mounting hardware on both boats, and purchased the unit all for under $500.
Hope this helps.