Have a look at this type of thing:
Theres more of these on ebay. Some need an input voltage some don't. Have a look araound.
You will need to use some diodes and a small capacitor to rectify the output voltage and the voltage will be small (3 volts or less). you may want to adjust your Aref pin to less than the default 5 volts to get better granularity.
But this unit isolates the high voltage and is much safer than other methods.
Also: http://forum.arduino.cc/index.php/topic,202828.0.html
Google the following:
TA12-100
TA12L-100
TAK17-02
TA17L-04
TA14W-100
TA17-03
TA17-04
TA17-05
to see which one is a best fit.