Remember Voyager 2? It will be crossing the termination shock Real Soon Now:

University of California-Riverside physicist Haruichi Washimi, using a computer model simulation, has predicted the Voyager 2 spacecraft will cross the termination shock "within the next several weeks."

Is anything still working on the Voyagers, or are they just hunks of metal at this point? (Pending their transfiguration into V'GER, of course).

What I really want to know is when/if they'll cross the Milky Way's galactic bow shock, which runs before us on our collision course with Andromeda.

And speaking of shock waves, there's a really big one playing over in Stephan's Quintet... not to be confused with the cosmic jam session going on in the Perseus cluster:

Sound has been detected from another black hole in the Perseus cluster, which was calculated to have a note some 57 octaves below middle C. However, the sound in M87 appears to be more discordant and complex. A series of unevenly spaced loops in the hot gas gives evidence for small outbursts from the black hole about every 6 million years. These loops imply the presence of sound waves, not visible in the Chandra image, which are about 56 octaves below middle C. The presence of the large cavity and the sonic boom gives evidence for even deeper notes -- 58 or 59 octaves below middle C -- powered by large outbursts.