As any nerd, I've always wanted my very own NTP server. Unfortunately the modules available are expensive (+$100) and very hard to interface when you're not much of an electronics guy. The next best alternative is without a doubt a 'Real Time Clock module'. It's a battery-enabled clock module that'll last a few years at a time (one site promised ~9 years pr. battery). I bought a couple from eBay and hooked one of them up to my Raspberry Pi. Now I have my very own reliable NTP server.
I'll soon elaborate on how I hooked it up, though it'll mostly be links to other sites, as I basically just followed random tutorials and advice from 'the big internets'.
So! If you need an NTP server, buy your own module or use ntp.Biggi.dk (or both!) :)