Try http://www.getspajobs.com. They post on twitter and their site - probably more that I am unaware of but they seem to have a strong following and response rate.
If you are a Day Spa Association Member, there is a free job listing board at http://www.dayspaassociation.com/employment/employment.htm. If you aren't a member but are interested in joining, let me know and I will get you some information:-)
I think a job listing board would be a good addition to this site too!