This metasite does an excellent job of providing links to museums' web pages worldwide. The site is supported by the International Council of Museums and maintained by Jonathan Bowen.
Users can submit sites for consideration, as can the museums themselves.
Some specialized search criteria include virtual exhibitions, history, science, technology, art galleries, children's exhibits, library exhibits, and computer-related museums. All sites are also listed alphabetically by country on the main page, and alpha by name within the country. These features make the site both browsable and searchable - both absolute musts for metasites these days. The site also provides mirror sites for easier access. Some of the sites are offered in both English and the country's native tongue.