If you find Darwin's Origin a bit daunting (I guess people both spoke and wrote in a different style back then), check out The "Origin" Then and Now: An Interpretive Guide to the "Origin of Species" by David N. Reznick & Michael Ruse.

And if you're interested in evolution, read "Your Inner Fish by Neil Shubin.

Also very much worth a read: "Endless Forms Most Beautiful: The New Science of Evo Devo" by Sean B. Carroll (evolution through the lens of developmental biology). Caution on this one: the illustrations in the hardback are so remarkably good that it's worth the hassle of taking it out from the library - or springing your your own copy.