My longest was around 4 hours... It's a great sensation ! My average is around 1-2 hours, very often.
Another thing I like to do is masturbating and edging a lot a time in the day, without allowing me to cum. It gets me super-horny ! Then during the night, I edge a little more and after a while I go all the way by cumming. These are one of my best orgasms ever ! However, it is quite difficult to do since you need to have enough time during the day...
Trshaver, I can ejaculate without orgasm too by masturbating and stoping really right after the 'non-return point'. I then see the cum flowing without having all the sensations of an orgasm, and can after continue jerking off.
Actually I discovered this one time I was edging and failed^^.