Well, it's hard to think of anything <i>radically</i> unique. But some memorable things that come to mind:<p>- the way Graham, Knuth & Patashnik's <i>Concrete Mathematics</i> has the students' comments, silly or enlightening, in the margins. Its also very well designed and put together.<p>- I absolutely love the design of Sedgewick & Wayne's <i>Algorithms</i> (4th ed.) The fonts, colour palette, diagrams illustrating algorithms etc, are all miraculously awesome. The next algorithms book I looked at seemed so tedious and incompetent I wanted to complain.<p>- I love raganwald's <i>JavaScript Allongé</i> apart from the pictures. But there are pictures throughout of coffee, coffee machines, coffee bushes etc with coffee-related captions, all totally unrelated to the text, that somehow work, like a breath of fresh air through the book.<p>- Needham's <i>Visual Complex Analysis</i> is a marvel of clarity in word and picture.<p>- <i>Eloquent Javascript</i> (I read the online version[0]) is impressively well-designed. A good mix of covering-the-basics and projects. A clean, simple and beautiful form.<p>[0] <a href="http://eloquentjavascript.net/" rel="nofollow">http://eloquentjavascript.net/</a>