4 Freedoms Relationship Tantra
Information and workshops on Tantra
http://www.tantra-sex.com/

Abbys-Sexual-Health.com
Has excellent articles and advice about various sexual activities and sexual health.
http://www.abbys-sexual-health.com/

Body Electric School
Well-recommend classes in bodywork and erotic education. Classes for men, women, gay couples, and straight couples. Popular classes include Tantra and spiritual sex. Based in in the SF Bay Area, classes are offered nationwide.
http://www.thebodyelectricschool.com/

Celebrations of Love
Tantra information
http://www.celebrationsoflove.com

Cleo Dubois Academy of SM Arts
Offers classes for individuals and couples in skills with BDSM participants and their accessories.
http://www.sm-arts.com/

Clitical
A good web site about female sexuality, including anatomy (with pictures), female masturbation, sex toy reviews, and other sex topics
http://www.clitical.com/

How to Have Good Sex
Various “how-to” topics online; the “techniques” section is especially useful
http://www.howtohavegoodsex.com/sex.htm

Jackinworld.com
Very comprehensive site on male masturbation
http://jackinworld.com

Koi Sex Tutorials
Good basics here on oral, anal, vaginal, masturbation, and positions.
http://very-koi.net/projects.htm

Let’s Masturbate
Masturbation tips and techniques
http://www.letsmasturbate.com/

Sacred Space Institute
Workshops and Conferences on Polyamory and Tantra
(415) 507-1739
http://www.lovewithoutlimits.com/

Sex Tutor
Tips on technique for various sexual activities
http://www.sextutor.com/

SexInfo101.com
Tips on technique for various sexual activities, and general sex information
http://www.sexinfo101.com/

Society for Human Sexuality
An informational website with sex and relationship tips and how-tos, reviews of books and videos, and guides to sex-positive resources and events in several major cities including Seattle, San Francisco, Portland, and Vancouver.
http://www.sexuality.org

The-Clitoris.com
A site dedicated to women’s sexual pleasure and health, with an emphasis on pleasure anatomy.
http://the-clitoris.com/

Toys in Babeland
Women-owned and oriented sex-positive toys shops; stores in NYC, LA, and Seattle. How-tos at http://www.babeland.com/sexinfo/howto
http://www.babeland.com

The Ultimate Guide to Sexual Fantasy: How to Turn Your Fantasies into Reality by Violet Blue, published by Cleis Press [Buy]
Violet Blue discusses ways to expand your sexual reality by learning how to ask your partner for and ways to engage in a wide variety of sexual fantasies.
ISBN 1573441902