I had the same issue with my husband when we were pregnant with our last baby. We didn't know the gender either but I had learned a lot about circumcision and decided it was something I did NOT want our son going through.
Anyway, we did wind up with a son and thankfully he is intact and we are both on the same page.

The things that brought my husband over were somewhat because of the logicalness of a. there not being any medical benefit b. no religious benefit (we're not jewish) c.the irony of mutilating something that is perfectly formed.
Now that is the typical arguments and why those did effect my husbands decision what really brought him over were these two things.
This question was posed to my husband (who was also mindlessly circ'd for the same reason...to look like everyone else.
1. If your parents hadn't of circumcised you would you go to the doctor today to have part of your penis cut off just to look like other men?
His response was H*ll no! There was no way he'd let a doctor chop off part of his manhood.
Point #2
2. We have both agreed that we do not believe we have the right to make changes to our children before they are of the age of consent. The only other good example I can think of right now is piercing our daughter's ears. We had both decided that needed to be her choice when she was old enough to be accountable and responsible for that decision since it was *her* body. This is in no way any different. How could we as parents make such a drastic choice for our son based solely on a personal aesthetic preference that was both permanent and brutal?
3. I had never and my husband had never come across the information on how circumcision effects sexual pleasure and once we both read that information my husband (and I) were pretty crushed. It made him really angry that he was circumcised at that point and it was a really big deal to him. He was depressed for a few days afterwards. I think this is important for men to learn and I think most men can connect with this when the other reasons don't really matter to them. Men enjoy sex and when they find out that they (and their spouse) have been robbed from a fullness of what their bodies were intended to do they get very upset. So, here is the link that helped but please be aware there are some very graphic images and videos. It is completely educational however and is meant to be that way, but still...just warning you.
You click on the top ten reasons but on the homepage you can also scroll down to read...
Hmmm. Mothering won't let me link it here because of the URL name. Just google: sex as nature intended it. which is also the .com name.
Here is another good link that talks about the effects sexually:
http://www.cirp.org/library/anatomy/ohara/