When you write a css property in the right-hand CSS panel then tab across to enter a value, it would be handy, by pressing up/down on the keypad, if you could cycle through the possible values for that property. For example, if I wrote the css property "text-transform", hit tab to set a value and then pressed up/down, it should cycle through the values: normal, uppercase, capitalize etc. This is functionality available in Firebug which would be beneficial to developers.
While it may not be very discoverable, you can hit Ctrl-Space to bring up a similar list of suggestions for valid property values whenever applicable. Then you can use the Up/Down keys to alter between available options and see them reflected in the page in the real time.