I already talked about how much I like the Asimov "How Did We Find Out..." series. They are the catalyst that made me realize I could do the course because his books provide a great representation of the sequence of important discoveries.
Another book series I'd like to recommend is the "How and Why Wonder Books" series. They have entries that are science- and history-based. I've investigated a number of the science books. While they are not heirarchially based, like the Asimov series, their optimism and their undiminished respect for human accomplishment (in the ones I've read) have been very impressive. They often have a good introduction to the topic that may put it in historical perspective before diving into the meat of the matter.