This is the book that a few LQS's have used for years for their Intro to Quilting/Beginner's class (because they always want you to buy a book :-)).
http://www.amazon.com/New-Sampler-Qu.../dp/1571200118
But really, the blocks can be as simple or as complex, small or as large, as you want. Heck, I guess some would even consider Dear Jane a Sampler Quilt.
Here are some images - just google "sampler quilt" and choose images instead of web. :-)
http://www.google.com/images?q=sampl...w=1280&bih=610