animation help

Can someone help me. I would like to know how to do these kind of animations with the flashing text.

http://i13.photobucket.com/albums/a273/Miss24CTU/buffybutton.gif
http://gillian.redux-angel.org/gax100a.gif
http://i11.photobucket.com/albums/a157/laaur3/AssManagerLaura_ATG.gif