When I am about to masturbate, I usually pump my libido up by watching porn (nothing very unique there, is it?)
I always been a fan of http://www.thehun.net for that purpose. It seems no matter what I'm in the mood to fantasize about, it's right, there, ready for me enjoy while I drop my panties and rub my little clit.
Quite predictably, I mainly enjoy clips of anal sex, even more so when there is spanking or hair pulling involved. I wish I could explain in details what turns me on about the idea of a man treating me like a worthless whore and forcing himself on me, while degrading me, but alas I am not sure I fully comprehend all the mechanics of that fantasy myself. But then again, it is quite delightful to watch on the screen.
And yesterday, while I was pinching my nipples and rubbing my clit hard, I was on the verge of squirting when I noticed that my pussy wanted to be filled, but not by merely a rock hard cock: I wanted to fill more full... I wanted a whole hand in there. I started cumming (and squirting) when I started to think about how wonderful it would be to be fisted right there, with the vibrator up my ass and my clit being abused very hard.
The kind of orgasm that leaves you shaking and moaning for a good 5 minutes after the fact. My kind of orgasm. ;)