There is an old thread on top of this category here, but the basics mentioned in the 1st post are still valid:
http://http://www.prepaidgsm.net/for...ead.php?t=6713
An updated survey of the 4 operators, some resellers and their data offers, you can find here:
http://prepaid-data-sim-card.wikia.com/wiki/Italy
About Wind: They can offer the cheapest data, but are the worst of the 4 networks what coverage and speed is concerned (according to net tests). As long as you stay in the cities and don't need high speeds, they can be still an option. Wind allows tethering, so hotspot use is no problem.