There is plenty of options available to you. To name a few...
http://www.clementfocuser.com/
http://www.focuser.com/
http://www.starlightinstruments.com/
http://www.fli-cam.com/digital_focusers.htm
http://www.optecinc.com/optec_015.htm
http://www.robofocus.com/
http://www.jimsmobile.com/menu_focusers.htm
You need to workout whether you want something in your optical path or out of path. What level of automation do you want - full automation can takes sometime to set up, but is really the most accurate for imaging (especially if you have filters which are not all parfocal - such as a Ha filter compared to a RGB set). You'll need a PC available for automation. Do you need temperature compensation, backlash compensation etc etc. For casual observing, just about anything will do the trick (well almost anything). You also need to ask how much budget you have. Focusers like the FLI PDI is expensive as it does not increase the backfocus much. Perhaps further research is required.