What are you looking for? Red LED's make good eyes. Use them directly for sharp points of light. Use them indirectly (lighting up the socket of a skull so you cannot see the LED directly). Or to get more of a glowing eye, maybe a red LED in a ping pong ball. Just some ideas.
Yes, typically a 9 volt battery with a resistor in series. There is a lot of information available on how to wire LEDs and what size resister to use, for example this forum has http://www.unpleasantstreet.com/forums/showthread.php?t=810&highlight=LEDs
If this isn't enough info I know of a good LED how-to (I think the site is Wolfenstien or something like that) I get a link to you tonight when I get home.