'Twas brillig, and the slithy toves did gyre and gimble in the wabe

Well, personally I'm a big fan of Slackware. If you know Red Hat, you know Red Hat. If you know Slackware, you know Linux. This is because Slack doesn't include ANY fancy graphical config and so on: you're working in the guts of the system so you can see exactly what goes where.

Ubuntu is often recommended for newbies to linux, but since you've got me and Nick in house as of September, and you're not clueless on the 'internals of the comp-yoo-tar' bit, I'd personally recommend Slackware. Trial by fire, and all that.