Pen and tablets are fairly cheap these days, 50 Earth credits will get you one, I use a UC-Logic which is getting on a bit but still works great.
Blender is getting more complete and amazing by the minute and Jaz Haz is exactly right, that's what I use for the asteroids, and indeed my attempt at a face did look like an allergic reaction
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I sculpt the high poly model then duplicate the .blend file under a low_poly name, than I use the 'decimate' modifier to simplify the model down to as few poly's as it will take without looking too obvious, then you unwrap the low poly model for the UV layout. Next you upload both the high and low poly models into xNormal to bake out the normal-map information that gets mapped to the low poly UV layout. Blender can also do this but xNormal is dedicated and gives better results, although Blender may have been updated by now. With xNormal I also bake out ambient occlusion and a height-map, the ambient occlusion helps with the texture and the height map goes into the normal-map's alpha channel for added parallax.
It's quite a fiddly process hence I don't often feel like emersing myself in it, but I would like to get at least one spaceship through this mill at some point, and considering there are curves all over my designs it would have to be done this way.
There are an awful lot of video tutorials on youtube worth browsing.
EDIT: I'll scan and post my initial castle scribbles, none of which are very good but just toying with directions, but it's all good to share these things
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