A quick google image search shows plenty of alternatives - I especially like the ones using plasma balls

It's just a giant generator thingy, so as long as it's close to the right size and looks electrical, you can do whatever you like. (Non-imperial ones, e.g. ork or chaos or necron, would be particularly amusing to model.)
if you really want to base it on
GW stuff, the Manufactorum kit (from Cities of Death) would be the obvious start.