Music and CDs
There are a lot of CDs released under the Houshin Engi title, and a decent chunk of them are drama CDs. We'll list a thumbnail gallery below of any we're aware of.
Soundtracks and Image Songs
The soundtracks contain short versions of the opening/ending and quite a few (20ish) background tracks. Many of these background tracks are doubled up, meaning you'll get more than one 'song' in a single track. The Image Songs are a collection of songs sung by the voice actors of different characters. It's a neat little collection with some pretty decent music.
Drama CDs
A Drama CD is basically where the voice actors come in and act out stories, usually scenes in the manga that weren't animated. It even has music and sound effects, so it's kind of like watching the show without the video. A lot of people enjoy this simply on the basis of seeing manga scenes given new life.
Singles and Small Albums
Singles are CDs that usually have 2-4 tracks, typically of the opening/endings of the anime. The Chihiro Yonekura album (larger image) also includes some other songs, but the track list is still relatively small.