I found a cool holiday tracking program last week http://whosoff.com. Lovely full feature program for tracking holiday allocations and requests for a small company. It has a proper approval system and lots of nice support for things like sick leave and pretty cool reporting tools. Best of all its free (ad supported, but ads are pretty innocuous).
Its a bit twitchy in Firefox (some gifs aren’t laid out properly) but apart from that does exactly what it says on the tin, tells you who’s off today.