Imagery
Different imagery techniques are used in many different types of therapy, for many different purposes. It is often claimed that imagery work can lead to changes in felt emotion, and that it can be especially useful when clients are stuck using cognitive techniques alone "I hear what you're saying, but I don't feel it".
Imagery rescripting
Imagery rescripting is a particular type of imagery frequently used in the treatment of symptoms of PTSD such as flashbacks and nightmares. There is also evidence that it could be useful in the treatment of intrusive images in other conditions including depression.
Imagery Rescripting Type A - negative image transformed into positive image
Imagery Rescripting Type B - new positive image constructed to rescript negative schemas
Description & examples of imagery rescripting 
Download from CommonLanguagePsychotherapy.org
Smucker's original paper on imagery rescripting Download from Mervin-Smucker.de
Imagery Rehearsal Therapy (IRT)
Often used for treatment of trauma-related nightmares
Exposure, Relaxation, and Rescripting Therapy (ERRT)
Compassion Imagery
The image of 'the perfect nurturer' is often used in Compassionate Mind Therapy (Gilbert / Lee)
Instructions for building a compassionate image Download from CompassionateMind.co.uk
Rewind Technique / Visual-Kinesthetic Dissociation (VK Dissociation)
The rewind technique is frequently used by practitioners of NLP. Although there's not much scientific evidence for the effectiveness of NLP in general the rewind technique shares commonalities with other forms of exposure therapy and so is inlcuded here.
The Rewind Technique Download from PsychologyTools.com
(Dr Mike Heap provides an excellent review of NLP on his website)
Reviews
Holmes, E. A., Arntz, A., Smucker, M. R. (2009). Imagery rescripting in cognitive behaviour therapy: Images, treatment techniques and outcomes. Journal of Behaviour Therapy and Experimental Psychiatry
Long, M. E., Quevillon, R. (2009). Imagery rescripting in the treatment of posttraumatic stress disorder. Journal of Cognitive Psychotherapy, 23, 67-76.
Evidence - a selection of studies testing imagery rescripting procedures
Arntz, A., Kindt, M., & Tiesema, M. (2007). Treatment of PTSD: A comparison of imaginal exposure with and without imagery rescripting. Journal of Behaviour Therapy and Experimental Psychiatry.
Brewin, C. R., Wheatley, J., Patel, T., Fearon, P., Hackmann, A., Wells, A., Fisher, P., Myers, S. (2009). Imagery rescripting as a brief stand-alone treatment for depressed patients with intrusive memories. Behaviour Research and Therapy, 47(7), 569-576
Smucker, Dancu, Foa & Niederee (1995) Imagery Rescripting: A new treatment for survivors of childhood sexual abuse suffering from post-traumatic stress. Journal of Cognitive Psychotherapy: An International Quarterly, 9(1), 3-17.