Once you've found an appropriate forum to post in, the best post would be a simple invitation to your site with a very brief, non-salesy description of what someone might find there. Save your sales pitch for when visitors arrive at your site. Commercial-sounding posts are frowned on in almost all online communities, except for the posting boards reserved for commercial announcements. Your announcement will get lost in the noise on commercial boards so it's best to let your Web site do the talking and your post do the inviting of the right audience.
Aliza Sherman is an entrepreneur and author of Cybergrrl: A Woman's Guide to the World Wide Web (Ballantine Books). She is currently working on her next book and new company.