On the visible bits (rocker cover, plenum, fuel rail) A wire brush will bring it up well, using a dremel will take a long time though!!
If you went down the route of powder coating they will sandblast it for you and it's not as expensive as you'd imagine. If you don't go for powdercoating I'd still take it to a sandblaster as it's quite difficult to get to some of the bits round the lettering
I'm in the process of doing mine so I took it into work and did it with a wire buff and even that took a good while to do everything.
For the rest of the engine, gearbox etc I have bought engine degreaser and was going to give it a good scrub with that and scotchbrite.
One thing to bear in mind. If you do go down the powdercoating route make sure you scrub the insides of plenum etc afterwards. A mate of mine has just had the inlet manifold on his scooby done and there was loads of carp left inside after.