I like the self assignment idea. I did it when I first bought a DSLR and shot only with the Canon 50mm f1.4 for a few months.
I purchased an 85mm f1.8 a few weeks back and took it on a stroll through downtown Utica NY while my car was fitted with a new windsheild. Here are a few of the shots:



I let the shutter speed drop in a few of these.
The first is the new chandelier in the Stanley Theatre, and the next is a path at a church, shot through the fence.