best one out right now for a decent price would be the Garrett AT Pro. 10' water and anywhere on land. you can snag one for about 600 new. I'm personally not a big Garrett fan, but for land and water hunting it's one of the best... unless you want to spend $2400...then you grab a Minelab CTX3030..... great in the water and is a killer on silver in the ground....
http://www.garrett.com/hobbysite/hbby_at_pro_main.aspx the AT pro is an excellent "starter" water/land detector...
http://www.minelab.com/usa/products/treasure-detectors/ctx-3030 this machine is pretty tech.. you can program different patterns.. you can connect it to your computer and download/upload programs from websites.... you could spend hours and hours figuring this thing out....