In Italy I use a wind sim - I pay 20 eur/mo. to get 10GB traffic (new users should pay only 10 eur for the first 6 months); you can also have 1 GB for 9 eur/mo. or 250 MB/week for 3 eur/week or 50MB/day for 1eur/day. If you get over your limit, you don't get billed, but speed decreases drastically; at that point, you can choose to renew your data credit even before the month is over.
Also 3 Italy has a good plan, 5 eur for 3GB/mo. but you must avoid roaming otherwise you pay much more for the byte.