All about Steins;Gate

OSTs

Besides the music from the anime, visual novels and movie, there are also bonus CDs and the beautiful Symphonic Reunion.
A compilation of all Science Adventure music is listed very nicely on the /r/steinsgate wiki.

Character songs

Drama CDs

The drama CDs are short audio-only stories recorded with the same voice actors as in the anime and VN.
Some were subtitled by Reading Steiner and uploaded to his Youtube channel, but it was taken down. They have however been reuploaded by JD2390 or can be downloaded from Link3693's mediafire.
A useful document was put together by /u/Brickorblock containing synopses and more detailed information about all Drama CDs.

Drama CD Alpha: Babel of the Grieved Maze

A story from Kurisu's perspective taking place before Okabe travels to the Beta worldline. There also is a translated manga adaption and an untranslated light novel.

Drama CD Beta: Arc Light of the Point of Infinity

A story from Mayuri's perspective taking place at the end of the anime and visual novel. The manga adaption is the process of being translated.
It has been partly translated and animated to look like the visual novel by Sarkkoth on YouTube.

Drama CD Gamma: Hyde of the Dark Dimension

A story from Okabe's perspective in the gamma attractor field, where he finds himself in a difficult situation. This is currently the only title that takes place in the Gamma Attractor Field.

Movie Bundle Original Drama CDs

These Drama CDs take place before and after the main events of the movie. Only the second one has been fully translated.

Info:

Released: December 13, 2013

Comptiq Drama CDs

This series of Drama CDs was included with a limited edition release of the movie, and takes place in 2011.

Epigraph Trilogy Accompanying Drama CD

The Epigraph trilogy light novels were accompanied by a drama CD consisting of three parts: Epitaxy of the Projected Curved Surface, Pandemia of Artificial Machinery, and Arpeggio of Time Rotation.
It has been partly translated and animated to look like the visual novel by Sarkkoth on YouTube.

Info:

Released: November 9, 2012

Anthology Drama CDs

Two slice of life Drama CDs, the first about a cosplay party and the second about going to the beach (which is sadly untranslated).

Laboratory Members' Round Table Meetings

A Drama CD about the round table meetings in the lab which was included with a limited edition of the original manga. It has only been partially translated.

Untranslated

Some Drama CDs have not been translated yet, more details can be found on the Steins;Gate wiki.

Links: