The Advanced Stirling Radioisotope Program (ASRG) was just cancelled by NASA. This was to be the saving grace for Plutonium-238 availability, as it was a much more efficient way to generate electricity than classic RTG systems.
The European Space Agency has selected two astrophysics observatories as its next large science missions, overlooking every proposed planetary mission. ESA's current selection of planetary missions, however, means it will still be a major player in solar system exploration for the next two decades.
Plutonium-238 provides electricity to deep space missions, but NASA only has a little bit left. A new article in Wired highlights the disastrous consequences of no plutonium for use in space, something the Planetary Society is currently fighting for in Washington, D.C.