1. wristtherapy.com - This might appeal to athletic trainers or health care professionals who specialize in "sports-related" musculoskeletal injuries. You could develop a small "mini-site" to resell a product such as PRO-ICE and get a pretty good commission off of it. Or, maybe, strike up a deal with the before mentioned doctors and trainers to drive targeted and qualified visitors to their sites (a pay-per-click revenue model). Once you generate a following, they "might" be interested in buying it from you to prevent their competitors (who you would be getting to advertise also) from getting anymore publicity and exposure. This phrase did have 57 searches at overture.com last month (which isn't a large amount -- but suggests that their may be a small niche market for you to inch your way into).
2. electronicdogdoor.com - Very nice name. This is your diamond in the rough. You just need to polish it up and position it correctly and you could make some good money off of it. I wouldn't sell this name unless you got a $1000+ offer for it. You need to do some research on companies that sell this type of product and sign-up with their affiliate programs or if they don't have affiliate programs just strike up a joint venture with them to sell their products to your visitors for a percentage. Since this is a tangible product: 10%-30% of the net profits would be appropriate. Check out a site like:
http://www.electronic-dog-door.net as an example. I don't represent this company, am not affiliated with them, or recommend what they do in any way. But it's a source of finding the companies you need to contact. This name got 172,561 searches on overture.com last month (sounds inflated to me). But, there is definitely a market for this.
3. mirrorsex.com - As just a domain name, I think this name is pretty worthless (no offense). It has possibilities though. There is an amazingly large amount of people who have sexual mirror fetishes. They love to drape mirrors on the walls and ceiling of their bedrooms and watch themselves having sex. You could target this niche market by creating a type of newsletter that publishes stories related to mirror sex. As a bonus revenue stream, you could affiliate yourself with mirror manufacturers or resellers that would give you a cut of the profits for introducing your subscribers and visitors to them.
Good luck,
Chris