Plugin request: Text highlighter (string replace)

Hello,

Does anyone know of any plugins that replaces certain words with an alternative in the_contents? Like, if I write the word “Orangeknight” then the plugin will automaticly replace that word with something like: ‹abbr title=”Something”›Orangeknight‹a› or ?? into <img src=”/img/blabla.gif”>

Would be lovely if you could use a admin-page to modify the list.