Lesbian Relationships
http://web.archive.org/web/20100707150210/http://www.yoatzot.org/question.php?id=9164:
Wasting seed is prohibited. However, the Torah’s label of “abomination” is applied to the male homosexual act without specific reference to wasting seed (Vayikra 18:22).
Sexual relations between women are prohibited, at least on a rabbinic level. The prohibition is explicit in the Shulchan Aruch (Even HaEzer 20:2). Such relations are also mentioned in a negative context in the Talmud (Yevamot 76a).
Additionally, a steady lesbian relationship may be prohibited by the Torah under the prohibition of maaseh eretz Mitzrayim (Vayikra 18:3).
Wasting Seed
http://web.archive.org/web/20100707115712/http://www.yoatzot.org/article.php?id=121:
1] The withdrawal method of birth control is prohibited. This is derived from the story of Er and Onan (Genesis 38) where God’s displeasure with this practice is expressed.
2] Male masturbation is prohibited. This means that masturbation is not the method of choice when procuring a semen sample. Similarly, this practice cannot be recommended for the solution of medical problems without careful rabbinic consultation.
3] Barrier methods of contraception that do not allow the flow of semen into the vagina are prohibited. This is the problem with the use of condoms, which are almost never allowed. Some authorities feel that diaphragms and sponges also present this problem.
4] Producing a semen sample for diagnosis and/or treatment of infertility is not a simple procedure to permit within halacha. While there is room for leniency for the purpose of allowing the couple to have children, most rabbis will want some workup done first on the wife before allowing the husband to submit such a sample.