This is an ongoing issue for us too. Our older girls (15 and 17) definitely want the latest clothing, gadgets, makeup, etc., and we are working hard to teach them the value of $. It is a big challenge and still a work in progress for many reasons!
As far as clothes, we buy reasonably priced things, and if they want the name brand clothing, they are given the amount we'd otherwise spend and they have to kick in $. We are pushing our oldest to get a job, although at this point, there's probably not much left for summer.
Did want to say that both my kids buy some of their name brand stuff off of ebay, and I help the youngest sell her things there once she outgrows them too. (The oldest is fully grown and wears hers out!) Anyway, you can definitely find some of the "cool" stuff used on ebay, craigslist, even yard sales. And, I second the idea for Ross or TJ Maxx.
I also agree that a part-time job could help him afford some of the things he wants and teach about $.
We are also being more explicit about the budget as they get older, and explaining why we choose to spend $ the way we do, and this helps some, so hopefully that will work for you.