Here is a little on-line sketchbook featuring a number of programming language design ideas. Maybe someday it will be a big book, and maybe some pages in here will get adopted into a really popular language.
The skecthbook contains a number of pages, each on a particular topic. Each topic starts with a motivation for exploring this topic, is followed by solutions from existing languages, and finishes up with some commentary and possibly some new sytantic and semantic forms.