I love the American Apparel long-sleeve waffle shirt. You can't do it too much. If you wear a long-sleeve black T-shirt every single day, nobody's going to say, "That guy wears a long-sleeve black T-shirt too much."
If you're wearing a sweatshirt that says "Gap Est. 1969" on it, you've got a couple days of wearing that before someone goes, "Why don't you do some laundry?