The Omniseal is one good choice, another that I really like is the Aloksak. The Aloksak site:
http://www.watchfuleyedesigns.com/And just another site with some more info and uses on it:
http://www.argear.com/gear/graloksakwaterproofbags.htmlI've had the little ridges that make the seal on the Omniseals often get nicked very easily and make it much tougher to close. I haven't used the aloksaks much, just about a year, but I really like them. Much tougher than they look. I carry my phone and some other essentials in my PFD when whitewater kayaking.
Good luck,
Jason