KayakingAfter the frequent attempts at Bribery, beatings, and simply getting towed at Sunrise - S-B opens the Kayak Forums
Also see http://www.ultimatekayakfishing.com
If you want to go low-end, there are bunch in the $100 range that will suit your needs just fine. Basic sonar only units, you could spend a little more and get color.
If you want to spend more and get a built in gps, I love my Humminbird 385ci.