As I've mentioned before, TalkOrigins is an indispensable resource in terms of its depth and breadth of information about evolution. But if I wanted to refer the someone unfamiliar with the subject to a single place online where they could get a quick, easy overview of the evidence, PhyloIntelligence would probably be my choice. It has a clean, appealing design, it's easily navigable, and it covers all the basic sources of evidence (genetics, fossils, evo-devo, etc). Some of the sections are a little short and could use expansion, but others are absolutely overflowing with compelling examples.
The section on observed evidence for evolution lists many instances where we've actually seen evolution take place directly, rather than inferring it from things like fossils and genes. The section on the age of the universe contains more than 30 ways that we know our world is old. Of all the sections of evidence, I think the one on fossil evidence might be the best. It contains its own subset of tabs, most of which include interactive timelines full of transitional fossils. Clicking on the "Man's Ancestors" tab showcases the closest known ancestors of humanity from 3.8 billion years ago all the way to the present. The "Tetrapods" section includes a really nice graphic of the gradual transition in skeletal structure from fins to fingered limbs.
What's really remarkable about PhyloIntelligence is that about a third of the evidence it presents comes from papers published in 2005 or later. Creationists are fond of claiming that evolution is a theory in crisis, and that the evidence for it is somehow disappearing. On the contrary, this site demonstrates that our understanding of evolution is increasing rapidly – perhaps more so than ever before.