http://www.isthisthingon.org/Yellowstone/daythumbs.php
Notably, a large one under Old Faithful about 2 weeks ago.
Also see smaller tremors under the Lake and Madison River from time to time.
Quake activity also seems to be taking a small step up.
A few moderate, shallow quakes occurred to just the west and south of the Park over the last month.
Something to keep an eye on.

http://www.seis.utah.edu/req2webdir/rec ... stone.html
http://earthquake.usgs.gov/earthquakes/ ... 131311.php