I took over the website for our PTO this year. I believe that a well maintained website can be a terrific communication tool.
Since I had some previous web design experience, I went a slightly different path than many here have; I purchased and installed a "portal" style software package that gives me the ability to update the site by logging in with my web browser, but I have much more flexibility than with the free sites previously mentioned. I can also give login accounts to other individuals (as many as they want) so they can update portions of the site I designate for them (again, through their web browser). This lets me and others make frequent updates to the site.
Sooner or later I may enable the "discussion forums" portion of the site (very similar to these message boards) if the parents and teachers are receptive.
It's still a work in progress, but so far, so good:
Zuni Community Association - Home Page
Although we don't use free hosting, our hosting costs are more than made up for by the revenue generated by the amazon.com affiliate store and links on our site. We direct our membership (and any friends and family they can enlist) to start at our website if they are going to make an online purchase through amazon.com, and a portion of each sale comes back to the PTO, paying for the website (with whatever's left over going into the general coffers).