I went to Monsterpalooza in Burbank, CA last year and hope to go again next year. It seemed to be geared more toward professionals in the special makeup FX business, but there was still plenty for fanboys and fangirls. I met Haruo Nakajima (actor inside of Godzilla suit and many other monster suits) and Doug Jones and the guy who was the Creature in The Creature From the Black Lagoon were there, too. Lots of makeup application demos, a horror/monster movies prop museum and lots more. It was smallish, (I saw everything there was to see on Saturday and went back on Sunday only to see Mr. Nakajima's panel) but it was a lot of fun.
I've been to a couple in jersey. Not bad. I usually go to horrorfind in Baltimore. But I think ima try to hit mad monster party in nc (close to home). I really need to go to one one the west coast. Shit I just need to make it out to the west coast soon.
Fright Fest here in KY is pretty cool. I usually find a few old monster toys and garbage to buy. Then they do a night at the drive in with horror movies.
Chiller Theater in North Jersey is the old school and probably best one. Monster Mania in Cherry Hill, NJ is 5 mins from my house. its gotten bigger in the past few years. I used to go to Horrorfind in Baltimore too, but I don't even know if they still do that one. Probably some others as well. Chiller is probably the best one in my opinion. I've met a lot of people that I never would have expected to. They have strayed from Horror a bit in recent years, but I think its cool-They get a lot of guests from old TV or ones you'd never expect to meet. I've met Pee Wee Herman and Ernest Borgnine at Chiller, Chatted with Mickey Dolenz, got pictures with Jane Weidlin. Its definitely a "fan" convention with a serious slant toward horror.