Hey, look what I found while checking out the Cosmos UI site, just out of idle curiosity. Action Button Colors, one of my all-time favorite addons, has been updated for Lich King, and it works. So do more of their other addons than I'd have guessed; if you like their components, check it out.
Here it is in action:
Tivara and Timmorn were hacking at a target dummy when I took this shot. You'll see that the button for Mongoose Bite is all red, because Tivara was out of melee range at the time. And you'll see that a lot of buttons are blue. Tivara ran through one Steady Shot after another until her mana was just about all depleted. Anything blue requires more mana to cast than she had the moment.
The nice large numbers, like 2 on Bestial Wrath, come courtesy of OmniCC, another of my favorite addons, by the way.