One of the things I enjoy so much about this hobby is the sheer creativity that some people have when it comes to conversions. If you've been reading the reboot of White Dwarf, you'll have seen the Blanchistu articles that cover some of the weird and wonderful conversions that he's either done himself, or has discovered in his trawls of the internet. Some of them are great, others are just interesting.
Years ago, there was semi-rpg/miniatures combat system called Inquisitor that allowed us to play a more story-like game with an inquisitor and his retinue, unfortunately the miniatures were about twice the size of normal GW models, so it was a pain to get hold of new bits to convert them with. Over the last few years there's been a growing trend of people playing something similar, but with normal GW figures. If you do a search for Inquisimunda or =I=munda on some of the larger gaming forums you'll find a load of very talented people.
The two people that I enjoy watching work are:
Migsula and his Legion of Plastic. I've been reading Migsula's work since he started on DakkaDakka and his use of a white undercoat has been the main inspiration for my more recent attempts; though I have to say that I've not quite grasped it yet as mine seem to come out all grainy; whereas his are nice and smooth. I suspect a better undercoat would serve me well here.
Jeff and his Officio Convertorum. He seems to be churning out some really interesting conversions at the moment that are making me want to dig out my bitz box and see what is lurking in it's depths.