And if you're a girl? Denim romper suits.
I've visited a few places that are well known for their clothes shops: Fifth Avenue, the Meatpacking district and Williamsburg (and other hipstery spots). Fifth Ave has Prada, Gucci, Ferragamo, Cavalli, Bulgari and their ilk. It was boring. The Diesel shop had a DJ in the corner. He had decks and Mac but was just fading from track to track. Some of the other shops were elegant, beautiful and spacious, but they're not really what I'm into. I'm convinced that there isn't something special about a $200 jumper that makes it better than a $50 one; you're just paying for the sofa in the shop.
The Meatpacking district was a little more exciting. Historically, factories where meat was packed were there. Then, for some reason competely unknown to me, high-end boutiques decided open up there. There are plenty of names: Diane von Thingyburg, Alexander McQueen and Louboutin are hustling for dollars down there. The more fun shops are ones that put together their stock themselves (not just selling one label). I was in The Jean Shop. They only sell like two cuts, but you can choose the material, wash, colour and distress yourself so you get a unique pair of jeans. Complete tosh, of course, but entertaining tosh nonetheless. Word on the street (ie, a newspaper article I read) is that they give you whiskey if you talk nice to them.
The hipster starving-artist places have fun shops. I was in a smelly thrift store in Bushwick while on an abortive attempt to visit a little art gallery. I think you'd need to have a strong sense of style and plenty of confidence to get dressed out of one of them. Also, patience to put up with having to sort through randomly stacked racks of shoes to find your size. It's really strange that so much of Brooklyn seems to have an incongruous mix of working class people that tend to be from the same background (all Hispanic; all black) and then the rich kids with their iced lattes in the middle of it. Some would label this as diversity, but I don't see much integration going on - the two groups don't mix any more than they have to.
Also, Urban Outfitters is the bee's elbows over here. The staff are soul-hurtingly well dressed. Get your shit together, people who work in Dundrum.