Are you researching housing projects by particular architects or in certain cities/countries? Or just curious about the possibilities for multi-unit housing? Check out the online resource HousingPrototypes.org. While currently limited to western Europe and a few other countries, the range of projects is impressive. Each project page provides summary information, a description, images, and reference works.
Here's the site's own description of its service: "Welcome to the web site dedicated to the study of international multi-family housing. HousingPrototypes.org contains examples of housing designed by different architects in different historic periods, countries, and cities. Projects range in scale from single buildings to examples of large social housing projects containing thousands of dwellings. A typological guide provides for research by housing site and building organization. Each example is presented as an individual case study complete with building data and description, a critical analysis, bibliographic resources, photographic images, and drawings. The data is cross-indexed for easy searching by housing type, country, city, architect and date. Links in the text provide for further browsing. New examples are constantly being added to this collection. The site is designed for convenient browsing and all examples are downloadable using most web browsers."