My best experience would have to come from my best friend's sister. This happened about a year and a half ago, and I still jerk off thinking about it.
My friend and his parents were out on vacation, so they gave me the keys to the house to watch their dogs, because his sister is away at college most of the time, only home on weekends. So the first day I came to feed the dogs, I watered and fed them, and sat down, disappointed I was finished so fast. I put my hand in my pocket and played around with my dick a little, since I was kinda horny. My cock was semi-hard, so I made my way upstairs into my friend's sister's room. I looked into her drawer and to my surprise I found a very skimpy white thong. I never thought that she would be the kind of girl to wear stuff like that, and it turned me on quite a bit. So I pulled out my dick and started to beat it slowly, thinking about her nice body, and how sexy the thong would look on her.
After beating it for a while, I sat down on her bed. A few minutes later, without hearing, she pulled into the driveway and opened the door. She'd forgotten something here over the weekend and came back to get it. I was so worked up in my jacking off I didn't even notice her walk in the door. I had my hand on my cock and my eyes closed when she walked in and saw me. I looked up at her and she looked back at me, we were both in shock. She looked down at my cock and commented how nice it looked, and asked if I needed any help. I just stammered in reply and she sat down on the bed next to me.
She slowly stroked my dick up and down, the precum oozing out of my head making a little slurping noise. After a few minutes of her stroking me, I felt like I was going to cum and I pulled away from her hand. She took off her shirt and unsnapped her bra, her medium sized breasts falling out. I cupped them and sucked on one of her nipples, moving my hand down to her pants and unzipping them. She kicked out of her pants and underneath, to my surprise was a little red thong. I kicked off my pants and brought my cock to bear again. This time her lips closed around the head of it and moved slowly up and down the shaft. It was absolute heaven, and one of my greatest fantasies: To get head from a girl in only a thong. I pushed her head away from my cock after a bit and slipped the thong down and began to work on her pussy with my fingers. It was absolutely soaked! I slid my lubed up fingers in and out gently until I felt her pussy contract and give a slight moan.
After she recovered from her orgasm I was hard again, and she pulled a condom out of her dresser drawer, which I rolled onto my cock. She pushed me back onto the bed and straddled my dick, riding me ever so slowly. Just before I came, I pulled out of her and removed the condom. She took my dick between her lips and her head bobbed up and down, very fast. I finally came in her mouth, which she gagged on a little bit, but got it down.
That was one of the best experiences of my life, and I still masturbate thinking about it today. Kara and I have hooked up a few other times, and we like to masturbate together, not so much as have sex.