Goto file in current directory

There should be an easy keyboard command to open another file in the same directory as the current one (or with a path relative to the current file). This allows a lightweight workflow for people who don't organize their files into projects.

This is the same idea I asked about on the forum -- I'm looking for an equivalent to :e or :tabe in gvim.

Ideally, this would auto-complete to files that already exist, but also allow typing a filename that does not exist yet to create that file.