I think Datumprikker.nl is one of the niftiest inventions on the world-wide web.  The site itself explains how it works:

Picking a date with a group of people can be a difficult task. Datumprikker.nl provides an easy solution to this problem.

In many cases you will need to make a lot of phone calls or send e-mails to find a date suitable for all participants. Create a event planner for your next meeting or event. Just select the possible dates and invite a group of people.

Everybody who is invited receives an e-mail with a link where they can easily respond to the suggested dates. As the administrator you can keep track of the progress and, once you have sufficient input, select the date.

The interface is very easy to figure out and use, and it really does save time (one of those things that the internet is always supposed to do but rarely actually delivers on its promises).  It's available in both English and Dutch.  I would heartily recommend this free resource (you can find the answers to some of the frequently asked questions here).  In short:  it's brilliant (and no, Datumprikker.nl is not paying me to write this post).

Just thought I'd pass along this little nugget that I've discovered and mined from the miraculous world of the internet...