A good place to find information about symbols is to use the Help menu in the Finder and type in a search for 'symbols'.
That will show you a list of all the common key names and their symbols used in menus as short-cuts.
Next, open System Preferences and go to the Language & Text preference pane and click the Input Sources tab and make sure there is a tick next to the Keyboard & Character Viewer. That allows access from the screen top menubar under the flag to bring up palettes which list many common and not-so-common font symbols. This works in OS X 10.6 - earlier versions access this slightly differently.
You can also use the Font Book application found in the Applications folder to see the repertoire of each font: that is, all the actual symbols/letters possible using various combinations of keys.
Lastly, click this link to see a fuller listing of French foreign symbols, and also as an access point to other web pages listing other languages/font/symbols.