Well there are some medicinal options. The thing that I can tell you will postpone your orgasm for certain, is SSRI anti-depressants. I don't know if they ever prescribe them for this purpose, but all the same I'm just letting you know that it does that. However, I wouldn't really recommend it. I've been on Paxil before, and I could fvck for like an hour and half straight, as hard as I could and still not get off. It's great for the girl, but sucks for you. Also, it could really screw your head up if not used properly. Anyway, just so you know and maybe want to consider it. I also think St. John's Wort is supposed to help with premature ejaculation.
The most effective non-medicinal methods that I know of is the start-stop technique and kegel exercises. You can do it with a partner or by yourself. Alone, you stimulate yourself until the point where you feel your orgasm starting to approach and then you just stop and let your erection soften and then start again. When I got off the Paxil it had some adverse effects and caused premature ejaculation. My girlfriend and I used the start-stop technique and I did kegels. I would fvck until reaching that point and stop for a few seconds until the approaching orgasm feeling subsided and then I would start again. Every time as soon as I would start again, I could go for as long as I wanted to. Eventually though, with the combination of the two you'll be able to go for as long as you want no problem from the beginning. I highly recommend it.