NCSE has a collection of free book excerpts. Check out the absolutely beautiful sample chapter from Charles Darwin’s Origin of Species: A Graphic Adaptation. It’s a stunningly gorgeous comic-book style rendition about Darwin and the theory of evolution. Also worth looking at is the sample from Alan Roger’s The Evidence for Evolution and the sample from Douglas Futuyma’s Evolution textbook.
In addition to this, there’s a very good online beginner’s guide to evolution from Berkeley University. Douglas Theobald’s 29 Evidences for Macroevolution is the best online guide to evolution. It’s a little bit wordy, but there are plenty of good pictures to hold one’s interest. I’ve written a post called The Evolution of Natural Selection that gives a basic understanding of how evolution works and some provides some history on the concept, tracing it all the way back to ancient Greeks. Nick Matzke’s Fun With Homonid Cranial Capacity Datasets shows a jaw-droppingly strong piece of evidence for evolution in the form of a graph showing human skulls from the past few million years. Neil Shubin’s article “Fish out of Water” offers up several fun and quirky evidences of evolution from comparing human anatomy to fish anatomy; I’d say that reading that free article will let you in on the best parts of Shubin’s book Your Inner Fish.
There are also a number of excellent videos online about evolution. Richard Dawkins’ documentary The Blind Watchmaker can be watched on Youtube for free. Youtube user CDK007 created a must-watch video called “Top 10 List Why Antievolutionists Are Wrong” which, along the road to destroying creationist objections, takes some interesting detours into explaining key evolutionary concepts and evidences. In fact, if you’re only going to watch one video on evolution and never read anything about it, watch CDK’s top ten list. It’ll be ten minutes well spent. Jerry Coyne’s lecture about evolution probably provides the best evidence for common ancestry summed up in only one hour, and so once you have the concepts of natural selection down-pat, looking at the evidence for common ancestry will be interesting and will make a lot more sense.
Last but not least, there are several good cheap (nearly free) resources on evolution. A ton of great books have been written on the subject within the past few years. I’d say that the two most compelling lines of evidence for evolution are genetics and fossils, and specialty books have been written on both of those: The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution and Evolution: What the Fossils Say and Why It Matters. Amongst the books that discuss several types of evidence for evolution, I think there are two that are tied for first place: Why Evolution is True by Jerry Coyne and The Greatest Show on Earth by Richard Dawkins. Each book has its advantages. Why Evolution has a knockout chapter about the evidence from embryos, vestigial organs, and “dead genes.” Why Evolution is the more concise (it’s only about 200 pages long) of the two, although I do appreciate Dawkins’ lengthier, beautiful writing too.