I appreciate that we can add custom search engines, but it'd be great if we could add custom DuckDuckGo-style !bang searches. Of course, using a prefix like DDG does may cause complications. Instead, how about just adding an optional keyword field in the manage search engines dialog. When the user types the keyword in the address bar, there can be a prompt to hit tab to switch to searching with the search engine represented to the keyword instead of the default search engine.
For example, I work with a JW Player's media hosting service quite a bit. A common task is to look up a video by its unique ID in the JW Dashboard. It requires a log in and would include the account number I use with them. The configuration could look something like this:
And then in use it'd look like
jwd <tab> 1234abcd <enter>
which would take me to