(Because there really needs to be a fresh thread.)
My vote for the best bridge across the Mississippi is the Centennial Bridge between Rock Island, Illinois and Davenport, Iowa.
3 reasons -
1. It is a beautiful arched bridge.
2. It has a safe, wide walkway/bikeway.
3. The Mississippi River runs east-to-west in this stretch -
So, there are beautiful bike trails along the river for miles on either side.
On a different note -
The best ferry across the Mississippi used to be the Golden Eagle Ferry.
Long ago - i.e. 1980s - they used one of the last side-wheelers.
Still operates - still pleasant.