I will second Varmint Hunter's recommendation, the Vero Vellini is a great sling for heavy rifles. Strong and simple and cuts the apparent weight of the a heavy rifle significantly. You can order them from Cabelas for 20 bucks. Also use Tactical Interventions, they are built about like a brick outhouse for tough - very comfortable for shooting prone. Buy direct from Mike Miller from his website. Another great sling is sold by Browning, it enables you to "pack" your rifle on your back like a backpack, arms go through individual straps and the rifle is out of the way and totally secure. Available from Cabelas also. Believe I covered that one some time ago, would be availabe through a search.
One of my friends has a fanny pack that enables him to set his rifle butt onto, takes the weight of the rifle nicely off his shoulders.
Vero Vellini for short hunts, day to day stuff. Tactical Intervention for shooting, toting and looking cool. Browning for long-haul type hunts.