My boyfriend and I are three years into a long term relationship. I have looked at this site quite often and have tried many of the techniques suggested. Jets in the bathtub, shower head, pillow humping - and all have worked great so I thought I would share my personal favorite.
My favorite way to masturbate is with a latex balloon. The long skinny kind used for making balloon animals. Depending on my mood I fill it partially full with warm water and moving it down to the end of the balloon and then tying it off (leaving a little empty space at the top). I am too embarrassed/cheap to buy my own vibrator or dildo, so this technique works great. It is clean because it is made out of latex and the feeling it wonderful. I usually warm myself up a bit by visiting this site or reading some erotic stories, by then I am wet enough that I am ready to start. I enjoy laying on my bed with my legs up against the wall with a pillow under my butt. I then rub the tip of the balloon around my slit and slowly slide it in. I am pretty tight so leaving room at the top allows for the water to move up and makes it easier to slide in. I then start moving it in and out of me at first slowly and then faster. If you want to cum quickly you can move your hands towards your stomach so the edge of the balloon is directly rubbing your clit. I prefer taking my time and pumping it in and out just so I am about to cum and then slowing down and pulsing the water into me by squeezing the balloon. I found my g-spot by tipping the balloon to the right angle and then pulsating on the spot. Other times I like to do it a little rougher and by squeezing and releasing hard and quickly (these balloons are surprisingly strong) it really simulates the real thing. Honestly I think by using this method I have become more aware of my body and what works best, so that when my boyfriend and I actually are together and have sex both of us can be extremely satisfied! You should try it - you won't be disappointed!