To chip in my two penneth, I've a dubious partiality for using a car-related theme:
scirocco.mydomain.com
corrado.mydomain.com
I know, I should get out more...:) Since the nameservers are only for my benefit and, on the whole, nobody else should ever need to refer to them, having names that are open to misspelling isn't really a problem for me. If this wasn't the case though, I'd certainly pick easier to use names that aren't as likely to be misheard or misspelt.
Until that day though, I've an entire range of VW cars to use!
R.