To begin with, clubbing as a lifestyle is just about the gayest thing you can do...but if you're travelling and you just want a ridiculous night club fix, there are a lot of places you can check out.
Vegas is insane, period. So is Miami. I've never been to LA, but I don't see how much else in the US could top Miami for a club scene. 
Mexico...go to Cancun, they have these crazy night clubs with lasers everywhere that are as big as football fields. 
Munich, Germany - P1's or P Einze, this place is nuts. We got in because we met the son of some local duke while we were hanging out in a pretty cool little bar. If you're not an international fashion model or a movie/rock star, you're gonna have trouble getting in. If you can though, it's worth it. Not the biggest places I've ever been to, but easily one of the most decadent clubs I can say I've witnessed. 
London, England - Also totally nuts, practically everywhere you go is fun. Just ask some locals for the latest sweetspot. 
Edinburgh, Scotland - Not really a huge club scene, but definitely some absurd places. In general, go to the grass market area and see what's up. It's just a beautiful city, so even the lesser clubs/bars are inside of gorgeous medieval buildings...totally ridiculous. 
Tokyo - far out. 
Seoul, Korea - Even more far out. Lots and lots of sick clubs. Lots of the best clubs and parties are underground sorta. One night we were hanging out with these girls and they asked if we wanted to go to a "house party." We were thinking that meant like some kid's parents were out of town or something. They took us to this gigantic townhouse in the fashion district and there were like 500 people partying their asses off in there. It was like an abandoned building and nobody who was partying actually lived there, but every night people would just show up. DJ's came and set their shit up and liqour companies would come with their samples and shit to do grass roots promotion. It was absurdly organized, never really seen anything like it. Super, super fun. 
Paris - no explanation necessary. Some of the most insane clubs ever. Used my girlfriend to get us into this place but I can't remember its name. Cillian Murphy, Jude Law, and Sienna Miller were there that night...outrageous...I was way under dressed. 
Obviously there are loads more, but these just stand out in my mind.Â