http://www.aglbic.org/resources/index.htm
This website of Association of Gay, Lesbian & Bisexual Issues in Counseling (AGLBIC), a division of the American Counseling Association (ACA), has very good collection of resources on counseling LGBT clients. 

Basic fact sheets:

Fact sheet on Homosexuality (from American Psychological Association)

Information brochure on Bisexuality (from Bisexual resource center)

Pamphlet on Transgenderism/Transsexualism (from Transgender nation)

Position Statements from Professional organizations

Overview of position statements from professional organizations (from religious tolerance website)

American Psychological Association (Policy Statements for Lesbian, Gay, and Bisexual Concerns)

American Psychiatric Association 

www.gmhc.org
A good website for gay men and lesbian women to know about their health-related information.

http://www.lesbianhealthinfo.org 
This web site is maintained by the Lesbian Health Research Center at the University of California, San Francisco, an affiliated research Center of the UCSF National Center of Excellence in Women's Health. This web site is a public service for lesbians and their practitioners about health-related topics specific to lesbians.

http://www.annelawrence.com/twr 
Medical and Other Resources for Transsexual Women. Contains a good collection of information for male-to-female transsexual persons.

www.biresource.org 
This web site contains health-related information for bisexual men and women.

http://www.transgendercare.com 
A good collection of information for all transgender people - male-to-female, female-to-male and cross-dressers.

http://www.gayhealth.com 
A website that gives gay health-related information and services.