Where to post online psychology studies for participant recruitment? A common challenge when running psychological studies is getting enough participants. 
Of course, there are many general strategies for recruiting participants, but I was specifically interested in forums and web pages that are specifically designed for posting links about online psychological studies.

For a given forum, are there any rules about what can be posted? is there any indication of the likely response rate?
Sites:


The social psychology network has a page for posting online social psychology studies. There are a range of requirements. In particular, it needs to be closely related to social or personality psychology.
SampleSize Subreddit is a community dedicated to completing surveys. They like it when results will be provided at study completion. It has close to 10,000 subscribers at time of posting. I have also seen posts to other subreddits such as the psych subreddit. However, such forums do not always react positively to such postings. If there is particular alignment between the topic and the reddit forum, then there is more likely to be a positive response.
Psychology Research on the Net is a site maintained by Dr John H. Krantz at Hanover College. It lists a lot of different studies.
Online Psychology Research UK contains several hundred studies and is maintained by Dr Kathryn Gardner from University of Central Lancashire. 
PsychStudies is maintained by Andrew Thomas from Swansea University.
Psych Forums has a section for posting studies to a section of their forum. However, they do require some form of payment for posting.


General observations


Most of these forums require that you have ethics clearance.


Other strategies


As @lmjohns3 mentions Mechanical Turk is a more general strategy
http://beta.cognilab.com/ looks like it might try to make the process of using Mechanical Turk simpler
Many general purpose forums on the internet have an "off-topic" section, which can be effective if the topic of the study is aligned with the topic of the forum. In particular, I have heard about people getting very large samples when posting research surveys to appropriately themed SubReddits.