How do I get Sublime Text's open-file GUI to show hidden files? I know how to tell Finder to show hidden files, but when I try to open a file in Sublime Text, the GUI that pops up do not let me see hidden files.  How do I tell it to show me hidden files?
You can press ⌘ cmd + ⇧ shift + . while the dialog is open, which will toggle show/hide hidden files.

In OSX 10.9 and up (Mavericks, Yosemite, ...) you need to be in the List View of Finder.