DRosedale, for your class C they make a shade that covers the windshield and side windows of the cab, here's a picture:
We used this on our class C quite successfully. It came with our coach, but I see they are quite reasonable at Rv Upgrades
, for example.
Of course it is opaque, so if you want something you can see through you can look at the solutions the other members have posted.
On our class A, we use the MagneShade Lori talked about and love it. For extra-hot or cold days (we use our coach all winter for skiing) we have a blanket which attaches to the magnets on the inside of the windshield with steel washers.