For you non-sentimental types, it's a bunch of free Portal 2 music.
The publisher posted "Volume 1" of "Songs to Test By," containing 22 tracks from the game. It also posted a set of six iPhone/Android ringtones made from recognizable soundtrack snippets. As a bonus, if you play them all at the same time, you'll hear exactly what this year's PAX will sound like. You can download the soundtrack from Valve -- or from us, right here!