These are freely available datasets from here and around the world. Some are accessible via API's, which are an automated way to mine data into software like Google Refine.

Data.gov.au - Is hosted by the Australian Government. At present it contains over 1000 datasets, including datasets on Construction materials, housing finance, planning, Property, and Transport. Contains a bunch of interesting apps and links to GIS software also.

Datacatalogs.org - Is a portal to open Datasets from around the world. API compatible.

Eurostat - Business and demographic statistics from the Eurozone. Also contains specialist datasets like rural development and land cover/use.

Statista - A wonderful data portal with an easy to use search interface. Contains a wealth of economic data, including Chinese real estate investment and construction, and some worldwide house price trends.

World Bank Data Catalog - A wealth of datasets from all parts of the globe. Contains World Development Indicators, World Bank Finances, Health, Education Stats Global Economic forecasts much much more! Largely API compatible.