Firefox Pro-Tip
I'm not sure if this is documented anywhere, but I stumbled upon a cool keyboard shortcut in Firefox 2.0. Control-Shift-T will restore (un-close) the last tab you closed. There is Mac version of this shortcut too, I think it's Apple-Shift-T, but I don't have a Mac handy and I can never remember the names of their stupid meta keys, so I'm not 100%.