Using Emacs to recursively find and replace in text files not already open

1. M-x find-name-dired: you will be prompted for a root directory and a filename pattern.
2. Press t to "toggle mark" for all files found.
3. Press Q for "Query-Replace in Files...": you will be prompted for query/substitution regexps.
4. Proceed as with query-replace-regexp: SPACE to replace and move to next match, n to skip a match, etc.
5. Press C-x s to save buffers. (You can then press y for yes, n for no, or ! for yes for all)

• M-x find-name-dired RET
  • it may take some time for all the files to appear in the list, scroll to bottom (M->) until "find finished" appears to make sure they all have loaded
• Press t to "toggle mark" for all files found
• Press Q for "Query-Replace in Files...": you will be prompted for query/substitution regexps.
• Proceed as with query-replace-regexp: SPACE or y to replace and move to next match, n to skip a match, etc.
  • Type ! to replace all occurrences in current file without asking, N to skip all possible replacement for rest of the current file. (N is emacs 23+ only)
  • To do the replacement on all files without further asking, type Y.
• Call “ibuffer” (C-x C-b if bound to ibuffer, or M-x ibuffer RET) to list all opened files.
• Type * u to mark all unsaved files, type S to save all marked files
• * * RET to unmark all marks, or type D to close all marked files

This answer is combined from this answer, from this site, and from my own notes. Using Emacs 23+.