The Zerg are basically a mod of the Tyranids
http://uk.games-workshop.com/tyranids/knowyourfoe/1/
Marines are almost exact copies, but honestly with less flair, of the Space Marines
http://uk.games-workshop.com/spacema...re-gallery/18/
And the Protoss remind me of the Eldar, but the comarison less obvious
http://uk.games-workshop.com/eldar/gallery/1/