Just came across this little ruby
right here. Cheap & easy. Tech specs
HERE.
It measures temp and humidity.
The above link even has Arduino library & sketch code to produce output like this:
This can affordably give you temp & humidity for every room in the house.
Also, if the code was included (don't know where that is yet) to calculate dew point, this could make hydronic ceiling cooling a reality for a home.
-AC_Hacker