I've gone on before about the idea of converting a multi-gear bike into being a "fixie". My main reason was that I was getting a new bike and it didn't seem like it was worth the money to buy a complete set of gears, chains etc. So my oft-mentioned brother-in-law did a conversion job for me.
The result is very nice. A simple bike which feels like it isn't going to go wrong. Lighter too. You have to make a bit more effort but he's set it on a low enough ratio that I can get up most hills without difficulty. When you go downhill you feel like a bit of a prat as your legs spin round at an alarming rate - but hey, I'm used to looking like a prat. Anyway, I said I'd take some photos, so here they are, hopefully showing the important innards: