This library dired-lis (dired letter isearch) let you isearch in `dired-mode'. You only need press letter like in TC(Total commander), not need press some keys to active isearch(in dired-isearch, or in dired-aux in emacs23, you need call M-x dired-isearch-forward or M-x dired-isearch-filenames to active isearch, but in dired-lis minor mode, when you type 0..9, or a..z , or A..Z(which you can customize), the isearch mode active automatically, and the letter is insert into isearch input area automatically. If you do not need letter isearch in `dired-mode', you can execute C-u M-x dired-lis-isearch-forward-always?, then isearch-mode active always even if you press enter in sub directory until you press C-g or other keys to abort isearch.
‘M-s f C-s’–
‘dired-isearch-filenames’: Isearch only among filenames.
‘M-s f C-M-s’–
‘dired-isearch-filenames-regexp’: Same, but regexp search.
‘M-s a C-M-s’–
‘dired-do-isearch-regexp’: Isearch the marked files.