What are trustworthy online websites to search for monthly apartment before visiting Italy?

For the Liguria area try www.liguria.angloinfo.com which has lots of info for the Liguria region including classified ads as well as a forum.  

 Or you could try www.secondamano.it

For Abruzzo you could try:  Abruzzo Villas

 Finding an apartment for a month, means that you are on holiday lets only, so real estate agents wont generally be able to help.  I would suggest www.subito.it or vivastreet for lets.   It depends on the zone - if you know where you want to stay you can zone in - most larger towns have a newspaper with classifieds or a listings paper. 

We've used Holidayrentals.co.uk for the last 4 years.  Didn't use it this year and the house wasn't anywhere near as good as usual.  Will be going back to using it next year!   I'd highly recommend them.  Many of the owners will do long-tem lets of several months to a year.

Hi! we are renting out our flat in the alps for the first time and we used owners direct and I hope it will prove a good choice. Believe it or not Ebay is a good site in Italy to look for properties too!Paola

I agree with latoca, Owners Direct are excellent.