I’ve recently being using BWToolkit for Interface Builder 3, and it’s awesome. Up until a couple of weeks ago it did have some rough edges; however, they’ve been smoothed off and it’s now a much more production ready toolkit. BWToolkit is created by Brandon Walkin from Marketcircle, the creators of Daylite, Daylite Touch and Billings. If you’re developing application for Mac, you must check it out.