Once you've used F12 to view your opened Dashboard widgets, it's a pain to have to grab the mouse and click the "+" sign to open the Dashboard bar to see the others.
Thankfully there's a keyboard shortcut: Command-equal. This will toggle the Dashboard bar on and off.
[robg adds: This seems to be yet another undocumented keyboard shortcut -- I searched Help quite extensively, and the only mention of Dashboard keys I could find was for F12. There's also nothing in the Keyboard & Mouse preferences panel. Unfortunately, once you have the dashboard bar up, there seems to be no non-mouse method of choosing a widget (anyone find a way?). Still, it's nice not having to reach for the "+" sign all the time.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050502142541362