There are many places to find information about upcoming DVD releases, including websites like MetaCritic, JoBlo and the DVD section of MovieFone. Each site allows you to view a calendar of upcoming DVD releases for months ahead of time.
These sites also offer information about upcoming Blu-Ray releases. For the JoBo site, you must specify "DVD" to narrow down the upcoming releases, and then scroll down to view movie releases by date. The MovieFone site operates the same way.
Metacritic gathers the Blu-Ray and DVD release information in the same place and posts it on the main page, along with the current MetaCritic score for that movie.