There was an interesting article in this last weeks New Scientist magazine entitled "Befriending the Body Snatchers" which talks about parasitic organisms that take over their host's brains. I can't find an online posting of it, but it talks about things like ophiocordyceps camponoti-balzani (
http://www.impactlab.net/2011/03/06/zombie-ants-controlled-b...), Gordian worms (
http://en.wikipedia.org/wiki/Nematomorpha), Entomophthora (
http://en.wikipedia.org/wiki/Entomophthora_muscae), sacculina (
http://en.wikipedia.org/wiki/Sacculina), and also the use of things like Beauveria Bassiana(
http://en.wikipedia.org/wiki/Beauveria_bassiana) as a way to fight malarial mosquitoes. Interesting stuff, now if only it was posted online... :(