Target has dress clothes, too, so if he already likes Target brands, you can try there. I have got my 12-year-old nice dress pants and shirts. They also sometimes have coats (so like a suit), but not always. They might have more right now for Easter.
I like Levi's dyed jeans for a nicer casual look. DS has some in navy blue, khaki, and gray. They are comfortable like jeans but look a bit dressier (for the school dance). They work well with polo-style shirts or sweaters when it's cooler.
I also agree with JC Penney. I've had good luck at H & M for my daughter, but never for my son. It's too trendy, IME/IMO.
DS '04 "Boogaboo"
DD '08 "Lilybear"