The Italian Natural Parks Portal
A useful overview of the various Italian national parks, with accommodation and campsite listings. Some parks, such as Etna, have posted walkers' itineraries too. The navigation leaves something to be desired, and the best way to find your way around is to click on the Regional Index link just underneath the map of Italy.
Alta Via di Monti Liguri
A rather impenetrable but admirably detailed guide to the Ligurian mountain route; unless you are a "well-trained excusionist" (as the site puts it) you may find it a daunting prospect.
CAI is the Club Alpino Italiano. It runs refuges all over rural Italy, many of which can be booked via e-mail. Non-members pay around £10 each night for a bed, members around half that - and you can join for 63 euros.
Long-Distance Hiking in the Northern Apennines
Well-written description of a family's trek from the Cinque Terre to the Tuscany-Emilia-Romagna border, with plenty of practical detail.
Agriturismo in Sardegna
A charming introduction to Sardinia's countryside, gastronomical specialities and farms willing to accommodate visitors. (Bed and breakfast generally costs around £10; full board around £20.)
Contrary to what its name might suggest, Best of Sicily is not a travel agent but an independent guide to the island intended for US travellers. It provides a basic introduction to Sicily's parks, lists a number of hilltop castles with the potential for steep climbs, and suggests a few walking itineraries around the Etna volcano.
You have to join an official group to climb the Stromboli volcano, which is still active. But the excellent field trips and tours on this site make an enthralling introduction to the island.
Bill Thayler's Gazetteer of Italy
It's worth typing in this very long address: Thayler offers no itineraries, but describes his hikes in Umbria and the Latium in considerable detail. You can also retrace Tobias Smollett's enjoyable trip through Italy, this time with photos: "to bed without supper, and lay in a pallet, where I was half devoured by vermin."