Oh man are we sharing mpd scripts? I have this one that lets me search through music directory and add anything to the play queue (so I can add a single track or an entire album or whatever):
There's also this one that lets me save the currently playing song to a playlist of my choice. It's good if I'm listening to a new album or a new artist and suddenly think "yeah, this song really fits with the mood of X playlist":
The sleeps are to prevent Cantata (graphical mpd client) from shitting itself if I run this script while it's open. Also notice mpc shuffle instead of mpc random on. It shuffles the current playlist, but keeps the linear play order, so that I can add songs to play right after the current one.
Oooh those are nice! I'll have to try mpc shuffle out then, and even though I generate my playlists with beets, I'll definitely try out the save to playlist one!