If you don't know what Balsamiq is you probably haven't been paying attention for the past year or so, or just don't read startup news all that often. Although

If you don't know what Balsamiq is you probably haven't been paying attention for the past year or so, or just don't read startup news all that often. Although they're not as well known as 37 signals, anyone that wants to start an internet business should know about them and their model.