One of the best ways that I've found to reach the big O is with an electric toothbrush. Like another person mentioned (the name escapes me) it seems like it would hurt but it honestly doesn't. If you're concerned, maybe try it with underwear on first to reduce the amount of friction.
What I do is lie on my stomach with my laptop in front of me so that I can read the stories here and get horny mentally (which for me is the best way). I then take my electric toothbrush and place it in my slit, bristles up and near my clit with the handle held under my stomach. Then I gently rock back and forward, allowing my clit to come into contact with the bristles. This doesn't lead to the best orgasm I've ever had but it's a quick and easy variation on everyday masturbation.