I was just shy of my 18th birthday, had been dating the guy for a couple weeks but hanging out for a few months already. He was my third or fourth official boyfriend, but I hadn't felt comfortable enough with any of them to do more than drunkenly make out. With this boyfriend though, it felt different. I completely trusted him and everything felt right, so I just kind of went with it. One night we were just at his house making out in his room and listening to music, and we both ended up naked. I didn't tell him it was my first time because I didn't want him to ruin it with questions/making sure I was fine/added pressure, etc.
It was actually really good, I didn't really enjoy the sex so much as being with him at the time, looking back I was probably just starfishing it and not doing a whole lot, but it ended up being like 20-30 min (listening to Zep II and Alexisonfire, I picked the tunes... nice)
We started doing it like 2-3 times a day for the next couple weeks, and then I told him that he had been my first. He was really surprised that I hadn't told him, but he said that it meant a lot that I trusted him so much. We ended up dating for almost two years (just broke up) and he's the only person i've ever been with. I don't think I could have asked for a better first experience.
Unfortunately this isn't a funny story (or as awesome as some of the previous posts) but for any of you who are still virgins: honestly, at least from a girl's perspective, it's waaaaaaaaaayy worth it to just wait and do it with someone you really care about.