Gosh! Don't everybody answer at once!
Ok, here are my thoughts on the subject. There is a lot of sensuality, both overt and innuendo, in the Bible. God wants us to have an exciting, satisfying sex life. I believe there are some limitations on what is allowed, though.
Anything done between one man and one woman within the bounds of marriage, provided both parties consent, is Ok. (Hebrews 13:4 Marriage is honorable in all, and the bed is undefiled: but whoremongerers and adulterers God will judge.)
I'd tend to agree that anything done TOWARD the goal of a marital relationship is pretty OK, too. After all, the whole story of Christianity is that man is imperfect, so we really aren't expected to be perfect.
While a threesome sounds like a blast, I'll have to pass. (but Matthew 5:28 says ...whosoever looketh upon a woman to lust after her hath committed adultery with her already in his heart) So don't think I think I'm better than anyone else, because I DO commit these sins in my heart.
We do use porn sometimes to help with the mood. I learned my earliest oral skills by watching a Girl-on-girl video. Truthfully, I don't care for g.o.g., but I figured I might learn something. My wife (then girlfriend) had told me that she was unable to come, but my first time giving oral, she had her first orgasm. I like to think I've gotten better over the years, too.
I believe the general teachings regarding masturbation are a horrible distortion of what the scripture was actually saying, so we happily ease our own stress when the need arises, or do it for each other's benefit.
Is that answer enough without sounding preachy?