Atlanta is considering a parking tax, with the conversation driven in part by this academic paper (PDF, 3.2M). The tax would help deal with a backlog of transportation projects, including an incomplete sidewalk network (sound familiar?) and potentially be used to match Federal dollars.
The paper includes a very interesting discussion of the relative merits of a transactional tax (a percentage of the parking rate charged, San Francisco charges 25%, Pittsburgh 50%!) versus a per-space tax. While both are almost certainly passed on to the parker, the latter is a pretty strong signal to property owners to consider uses for their real estate other than parking, since the tax has to be paid whether or not a market for the space exists, or is strong enough to cover the tax.
Another interesting aspect is the suggestion of a tiered tax approach with the highest rates at the city center, diminishing as you transition outward, in order to avoid shifting of parking demand to lower-taxed areas nearby.