Drush make project versions when there is only dev available?
If the project has both a stable release and a dev version available, you can force usage of the dev version using something like

projects[geocoder][version] = 1.x-dev


You can also directly pull the project from its Git repository with

projects[geocoder][download][type] = git
projects[geocoder][download][url] = "http://git.drupal.org/project/geocoder.git"
projects[geocoder][download][branch] = 7.x-1.x