Japan's Akatsuki probe, also called the Venus Climate Orbiter, will fly in an equatorial orbit between the atmosphere's top layers to an altitude of about 50,000 feet. It will study Venus' violent winds and acid clouds, and science instruments will look for signs of recent volcanic activity. It launched this summer and should reach Venus by December.
Cassini is the size of a small school bus. Imagine a Robot that big wheeling (or walking around mars). You could shove every instrument you ever needed on it. one step at a time I suppose. This new rover looks promising.