Edward Tufte
Edward Tufte is in many ways the darling of Web2.0. First coming into prominence a couple of years ago when his concept of 'sparklines' 1, 2 starting doing the rounds of the tech blogs, his manifesto for clean design and clear display of information has essentially become accepted truth. If you've not heard of him there is a fascinating intro over at NPR which will, like as not, lead you to seek out some of his books. We've got Visual Explanations here and it has been inspirational in times of IA doubt.