Wikipedia's List of Family Trees is exactly what it says...a compilation of notable family trees, including nobility and royalty, rich and famous families, important religious and historical figures, and many more.
An Ahnentafel-style family tree from Wikimedia.
They even have family trees for fictional families. If you've ever wanted to map out the familial relations for Scrooge McDuck, Luke Skywalker or Marge Simpson (and who wouldn't?), then this is the place.
Among the more intriguing family names you'll find here are:
Lady Astor and her brood, along with the Roosevelt family, from the US.
Dynasties from Egypt, Persia, Japan, China, Korea, Mongolia and the Aztec Empire.
The Nehru and Gandhi families from India, and Bhutto from Pakistan.
Family trees from the Bible, Islam, Babylonia, and the Greek Gods (an essential item for you Percy Jackson fans).
And lest we forget, there's the wonderful, recent work done on Michelle Obabma's family tree.
There's nothing in this whole collection that ties these historical figures (real or imagined) in any way to my own family. I imagine that's true for most folks. Still, it's a wonderful and interesting overview of who's who, and of how family trees get put together. Wikipedia also has a general article on Family Trees that is worth a read.
Visit the main page of Free Genealogy Tools for more, umm, free genealogical tools.
And don't forget to also check for your family history at Ancestry.com and NewspaperArchive.com. These are subscription databases, but they are among the most powerful research tools available for looking into family roots.