Clipboard Format Spy is a simple free tool which displays more information on the contents of your clipboard. This sounds a little basic and dull, yes - but there's more to see than you might think.
Highlight some text in Notepad, for instance, press Ctrl+C, and this doesn't just copy one item. Clipboard Spy lists a "text" object, "OEM" text, a Unicode version, and a Locale object which describes your text language. Double-clicking any of these displays their contents.
Now open Internet Explorer, visit a web page, then copy a mix of text and graphics to the clipboard. You still get plain and Unicode text copies, but this time there are Rich Text Format and HTML versions, with embedded graphics. An "msSourceUrl" gives you the address of the copied page, and again you can view any of these by double-clicking, or by choosing a specific option from the right-click menu ("View as binary", "View as text", and so on).
If you've a copy of Google Earth installed, launch it, browse somewhere and click Edit > Copy Image. You might expect the program to copy a single image to the clipboard, but in fact there are nine: two DIBs (device-independent bitmaps), and seven others in various formats (JPG, PNG, BMP, PPM, XBM, JPEG and XPM).
It's a similar story with some other graphics tools. Open your preferred image editor, copy something to the clipboard and see what actually gets stored (it's usually more than you'd expect).