Have you thought about putting him in an obedience class? Those are great for socialisation and training. Arthur is going to be put in school as soon as he's done with his shots. (He's a little behind because of the anti-biotics he was on.) PetsMart and Petco are good places to socialise too. With Charlie (and eventually with Arthur too) I found that if he started barking at someone I gave him a stern NO and made him sit. We didn't start walking again until he calmed down. Also, if at PetsMart or something keep a little bag of treats n stuff and if someone wants to pet him, have them give him a treat first.

I'd call your Parks and Recreation offices (or whatever they're called where you're at) and talk to them about starting a dog park. They're great to have around!