Dy4828,
I think that this topic must come up about once or twice a month and each time I have to reassure you fellows that a man's testicle are almost always not exactly the same and, again, almost always one is larger than the other. I have seen may pairs of men's testicles, as I am a massage therapist, and can tell you that I have never seen a situation where a guy's testicles were exactly the same.
I wouldn't think you need to worry, but if you are still really concerned than see your doctor.
Hope this helps,
Wendy