The most secure way to ensure future access to research data is to entrust data files to a stable, trustworthy online data repository. Some repositories accept data files that are specific to a discipline or to an institution such as a university, or may accept any data files associated with the research process. Repositories also typically provide an interface for others to search for and download research data, and even restrict access to data during an embargo period. And many repositories provide secure storage through a system of backups and checks that ensure long-term access and preservation. See the Repositories tab for lists of repositories.
The key to ensuring the continuing value of research data is to properly preserve digital files such that they can be accessed well into the future. This can be a difficult undertaking for an individual researcher. However, some academic institutions and non-profit organizations have created repositories, or online data collections, with preservation capabilities. In order to take full advantage of their capabilities, research data should be properly described and in a format that a repository can manage. More information on data preservation can be found in the links below.
The Library of Congress' full guide to preservation
Keeping Research Data Safe
Charles Beagrie's guide to assess the costs and benefits of curating and preserving research data
Geospatial Data Preservation
The National Digital Information Infrastructure and Preservation Program (NDIIPP) guide to preserving geospatial data
The Digital Curation Centre's guide to understanding digital preservation
Free, open source digital forensics software for libraries, archives, and museums
The NDSA Levels of Preservation
The National Digital Stewardship Alliance's (NDSA) matrix showing a tiered set of recommendations for digital preservation activities
Guide to Social Science Data Preparation and Archiving
The Inter-university Consortium for Political and Social Research (ICPSR) guide to planning data preservation and archiving activities