If you regret it in a few years, he can always have a reversal or something. My father-in-law did that and had another kid. We're also done over here. I had an IUD put in, but now I'm starting to feel all wacky with it in - nausea, headache, cramps. If I keep having these nasty symptoms, I'll probably have it removed and we'll be back at square one in regards to birth control.
It's weird, I was totally cool with only one kid after my son was born, but now I sometimes feel like I'd want another since I had my daughter and she's only 8 weeks old! What's up with that?