There are numerous excellent websites which provide information about Galileo. This is a selection of those I have consulted most frequently:
The Galileo Project at Rice University – lots of invaluable information.
What was the Institute and Museum of the History of Science in Florence and is now the Museo Galileo – by far the largest collection of resources. It used to be impossibly difficult to navigate, but is slowly becoming user friendly.
A remarkable page on Galileo's moon drawings:
Reenactments of Galileo's experiments by Paolo Palmieri and others:
Ms Gal 72 – Galileo's own record of his experiments:
A general website on the scientific revolution, by Robert A. Hatch:
A useful source of texts in Italian, although not, for the most part, the standard editions:
The first great italian dictionary, which records the language as it was written by Galileo:
There are quite a few copies of Galileo's original publications on the web. As a sample, here are some copies of the first edition of the Sidereus Nuncius (Venice, 1610):
The Linda Hall Library (which also has the pirated edition)
The Rare Book Room, which has a number of other works by Galileo:
Stanford Library copy:
Warnock Library copy:
The copy at the Museo Galileo (you have to enter search terms, and what will come up will be both the first edition, and, marvel of marvels, the manuscript)