Let's see... most memorable blowjobs...
1) Probably the most memorable - I was 21 years old, and had just started hitting the club scene. I hooked up with this 40-something cocktail waitress at a hotel bar, one of the few places in our city at the time that had a decent dance scene. Very beautiful, very hot lady. Amazing body. We went to her place and started drinking and making out. For several hours. She would let me touch her anywhere, and I made her cum several times with my hands and mouth, but she would NOT let me fuck her. I'd been hard for so long and was so ready to cum, it was painful. I'm not usually a quick cummer, but when she went down on me, I lasted exactly 3 bobs of her head before I started cumming. And cumming. And cumming. And unlike every girl before that, she kept my cock in her mouth, kept blowing me, and kept swallowing until I finally quit writhing and bucking and moaning and yelling. She was amazing. The pleasure about ripped my head off; I'm surprised I didn't ejaculate my whole prostate. Her name was Patty. I only saw her a few more times, but I'll never forget her.
2) Another memorable one some years later - a sweet girl by the name of Krystal. Much younger, very cute, very in love with me (long story). I wasn't really into her, but in a weak moment (I was in a relationship at the time), agreed to go out with her. We had lunch, a couple of drinks, and then went back to my car and started making out. She ended up giving me a blowjob. Very slow, very sweet, lots of technique. She was making me crazy, building me up SO slowly, but still steadily. She finally pushed it over the top, and I started squirting, but was only barely starting to feel my orgasm come on. My orgasm kept building, slowly and steadily, squirting the whole time, until I came so hard I almost passed out. A terrific blowjob, especially given her age (yes, way past legal...).
3) Most of my other really good blowjobs have cum from guys, though it's different without the emotional connection, and much of it has to do with the fact that they almost always swallow, whereas girls rarely do.