In reply to Sl@te Head: I recently picked up a rental car at Palermo. I booked via CarHire3000 and thy set me up with Maggiore. I got a free upgrade at the desk from a Panda to a Golf, which was nice. The fuel arrangement was "you get it full, bring it back full", much better than these ridiculous arrangements where you're supposed to bring it back with the same ~3/4 tankfull it had in when you picked it up. There was no extra charge for dropping off at Catania, either. Basic insurance was included in the rental cost. I always buy the additional insurance before I go, usually insurance4carhire or you can Google for others, or try comparison sites.
A word of warning: road signage in Sicily is bad verging on useless. Some places, usually the provincial capitals, seem to appear on every bloody sign - a bit like if Edinburgh appeared as a destination on every road sign in the Highlands. We got directed round three sides of a square one time, after I'd followed a road sign rather than trusted my hazy recollection of the way we'd come earlier that same day. We also got sent completely the wrong way off the SS640 on our way to Agrigento, an error which took nearly two hours and much swearing to recover from.
The poor signage was made worse by the fact that the only maps I could find before I went there were too large a scale to be any use for navigating in or near built-up areas. Due to a number of significant additions/changes to the road network, they weren't 100% reliable for cross-country navigation either. My advice would be to buy or rent a satnav, or if you have a smartphone you can use Google Maps (the latest version allows you to download maps before you set off, so you're not reliant on extortionate roaming data charges). Bitter experience also shows that it helps if someone in the car other than the driver can work said satnav/smartphone...
Oh, and if you're looking for a supermarket then they have a bizarre habit of having big billboards telling you that there was one in the town you've just driven
out of. Go figure.
Driving hassles aside, Sicily is a great place to visit and the people are very civilised and friendly. The seaside village we stayed in filled up with young people at the weekends but there was no aggro, everyone was happy, sensibly behaved, and having fun without making arses of themselves.
I'm sure you'll have a great time.