There's probably already a dozen different ways to do this with Emacs, with context sensitivity depending on how hard you try, what language you use, and if you're prepared to suffer CEDET.

See http://www.emacswiki.org/emacs/Yasnippet for one option, http://www.emacswiki.org/emacs/AutoComplete#toc2 for another, and various bolt-ons to Anything: http://www.emacswiki.org/emacs/Anything