I found this while banging around in the AVSForum. It's a free Java-based audio analyzer program that helps you set up your equalizer to handle your specific room and speaker characteristics. It runs on Windows, Mac OS 10.4, and Linux, using whatever (reasonable) sound card you have. It's very well-thought-out, ties into a typical Radio Shack SPL meter for input, and self-calibrates against the sound card in a loopback configuration. It runs a tone sweep and does an FFT analysis of the results, looking for peaks/dips, and will do impulse measurements. The real target appears to be for setting up subs in association with mains, but it does function up to 20Khz, so can be used in the general case too. if you happen to use one of the supported parametric EQ units, it will automatically download compensation filters to counteract the room.

See here: