I got fucked by a guy that had a curved dick. By the way it was curved, it was hitting my prostate perfectly each time he thrust his dick in or pulled his dick out. When he got going, it was constant prostate arousal. That was the closest I have gotten while getting fucked by a guy.
I also have a fuck machine and when I put the right dildo on it (one with a curve again) it will give me an anal orgasm. I will stand there getting fucked by this dildo that is hitting my prostate just right and I will have cum flowing out of my dick. It isn't as strong as a regular orgasm, but I can achieve it without using my hands, just the dildo in my ass.