Ask the recruiter at the company, "What do the programmers typically wear? I just want to dress appropriately for the interview." Then just dress slightly nicer than that. If they wear t-shirts and jeans, then you wear a casual button-up shirt and jeans. If they wear dress pants and button-up shirts, then you throw on a jacket and maybe a tie. It is all over the board for a programing interview depending on the company and location.