Gimme some ido... everywhere! This pacakge replaces stock emacs completion with ido completion wherever it is possible to do so without breaking things.
Get it from http://marmalade-repo.org/packages/ido-ubiquitous
Note that ido-ubiquitous is not enabled for org mode or magit mode,
because those modes have their own built-in support for ido, which you
should enable instead. Also, to enable ido for all file and buffer
completion, customize ido-everywhere
.