Is there a dashboard widget that has extended Unicode characters?
I couldn't find one, unfortunately. If you know the codes (which you can easily find from the web) you can enable the Unicode Hex input from System Preferences>Language and Text>Input Sources (it's near the bottom). That way, when you hold ALT, you can enter a Unicode symbol number for that symbol to appear.

Example: ALT+270E enters a ✎ pencil.