Are there any humidifiers available for sale that hook up to a
continuous water source that are designed for homes with baseboard
heat, i.e. they have their own built-in mechanism for distributing the
humidity as opposed to the units that go on forced-air home furnaces? 
I am tired of hauling water several times daily to fill up our stand
alone humidifiers.  We are currently using a Sear humidifier, see
http://www.sears.com/sr/javasr/product.do?BV_UseBVCookie=Yes&vertical=APPL&pid=03215412000
which requires a refill every four hours or so.

"Swamp coolers" are devices that provide evaporative air cooling in
arid climates. I wonder if one could be run unvented to provide
humidification. Anyone?

Cool mist humidifiers are essentially indoor swamp coolers.  As the
water is blown into the air, it evaporates and absorbs heat.  The
difference is that they don't use cold outdoor air.

I suppose you could hook them up the same way outdoor swamp coolers
with a continuous supply of water, but they would need some sort of
float valve to turn the water off after the reservoir is full - just
like with outdoor swamp coolers.  If I was mechanically inclined, I'd
invent one and market it.  I think it would sell because people hate
constantly filling up these humidifiers.  You feel like you're back in
the 19th century and hauling water from a well.  Also, people would
buy more cool mist humidifiers, because they would be more convenient.

Any inventors out there?  Also, surely someone has done this already. 
Come on Google, research this!

Finally found the answer myself by calling a plumber.  Aprilaire makes
a model for $289.  Note - the plumber told me it costs $1500!  Here is
a link http://www.iaqsource.com/index.php?module=product&prod_cat=0&prod_mfg=1&prod_sub_cat=0&prod_id=7