I have a few options for you.
Wiggy's waders,, they are the lightest option and NOT very hardy. Okay for quick crossing and such, but they will get holes. I just slap on some UV aquaseal and drive on.
http://wiggys.com/moreinfo.cfm?Product_ID=5
I'm wearing here to load the float plane.
The next option is more durable but weight is about 5 lbs.
Neo River Trekkers. If you go with these, make sure they will fit over your boots. I have to use a XL for my size 10 Lowas. Been using these for years and never had one leak. The soles are vibram, but they can get slick in cold weather as the rubber gets hard.
http://overshoesonline.com/rtk8/NEOS-River-Trekker-Overshoe-Hipper-Brown.htm
The 3rd option is what I use these day on mountain hunts.
Plastic boots, I use Kolflach, and wear barneys glacier socks. The socks are waterproof and can be rolled up and down as needed. make sure to size the boots to fit with the socks.
http://barneyssports.com/footwear/footwear-accessories/glacier-socks.html
Good Luck and I hope this helps.
Steve