David Beecroft: Beginning Improvisation 2 - Harmonic, Melodic Minor and Diminished.

Here is the second book of the Beginning Improvisation series designed for really working on a specific sound without the stress of chord changes.
If you find Aebersold's Volume 21 Gettin' It Together too fast and confusing, use this! The book and play-along CD provides a simple approach to getting the sound in your head and understanding what your hearing.
The idea is simple but the results are cool: provide an opportunity for beginning players to find their own melodies over the sounds that go into creating a jazz piece by providing a "play-along" track for each chord found in a song.
The idea goes a bit further by providing a simple preparation exercise that gets the chord sound in your ear. You may then forget about the chord tones and scale degrees and concentrate upon melodic ideas playing what you know and feel.