Boston University has a list of open business case study repositories. All are free and some are editable.
The Case Centre offers a large and diverse collection of management cases for purchase.
Darden School of Business at the University of Virginia has searchable collection of case studies online. Abstracts and video previews are available but you must purchase any studies that you want. Verified faculty have free access to all content on the site.
Stanford case studies are searchable online. Many of these are available for purchase through Harvard Business School Publishing.
While Harvard Business Publishing does not make all of their case studies available through a university-wide subscription, the library provides a couple of different ways to access some of them. In addition, it's possible to order them directly from the HBS website, for around $6.50 - $12.00 each.
The first way to access HBS case studies is through our subscription to Harvard Business School Case Studies and Core Curriculum. This EBSCO database provides access to over 2,000 case studies curated by editors from Harvard Business Publishing.
Search for cases using keywords or the title. Note that the search results will include documents from Harvard Business Press Core Curriculum, which provides access to readings that cover entrepreneurship, finance, accounting, marketing, operations management, organizational behavior and strategy. To make sure you're looking at HBS cases, look for HBS Case Study Collection in the results list:
In addition, you can find some Harvard Business School case studies in Business Source Premier. Harvard Business Review publishes one case study per issue. In the advanced search, select Full Text, enter Harvard Business Review under Publication, and select Case Study under Document Type. See image below.
You can find cases on the tech sector using IDC. To search for case studies, enter "case study" in the search box on the main page. You can then use the filters on the left side of the search results page to narrow down the case studies based on audience (tech supplier or tech buyer), document type, topic or region. 
The Financial Times has recently started publishing case studies, many of which concern sustainability. You can find these here or by searching for "business case":
Search the following databases to find articles dealing with your particular topic (e.g., employee empowerment and airlines). You can search specifically for case studies in some databases. From the advanced search in both ABI/Inform and Business Source Premier, you can select "case study" under document type.
