Pure paradise
Well, I think masturbation is paradise on earth. I mean you don't need a gal to enjoy sex. Just do it, with your own imagination.
A picture says a thousand words!
I visit one of my friend's websites where she has a lot of photos of herself posing in sexy swimwear (no nude photos though). I imagine her naked and stroke myself up and down. With some more imagination, I fantasize her kneeling in front of me, ready for a huge load of cum on her face and hair. I cum (for her) in no time.
Mind over matter
When I jerk off, I always imagine that somebody, preferably a woman, is giving me a blow job! When your power of imagination is high, the orgasm is huge too!
Skirting the issue
I like to make it last long. I wear some white shorts and think about sexy girls in miniskirts. I give them names that sound sexy like Stephanie or Louise and imagine them sucking my penis. This makes me wet with excitement and I like to lie on my front and slowly thrust. Don't you love that feeling? As I come, I say the girl's name and come in my shorts imagining that I am squirting and staining their miniskirts.
Golden oldie
I have a fetish for older women so I typically imagine fucking my mother-in-law or another golden oldie that I've come across.