System setup with UPS and USB HDD

I'm doing some planning before purchasing. I'm planning to have a RPi B board with an USB HDD (on an external usb-hub) attached for more storage and safe operation over longer period of time running 24/7 as a local install.

Today I'm using the Pico UPS for my home-control RPi which is running z-wave and 1-wire on a SD card.

I surely want a UPS for my upcoming EmonCMS RPi, I guess when having the USB HDD connected the Pico UPS will be too small. What are your thoughts or your setups ? Do you use some kind of UPS ?

Maybe a powerbank with some code/script that monitors my other RPi or maybe the ethernetconnection for "powerfailure" status... ? Or a "real" UPS.