Alfred's been pretty good Mac-side.
Shame that Synapse & near as I last saw Gnome Do seem to have also died off Linux-side.
It's a useful product space.
http://tools.suckless.org/dmenu/
Pipe a list of things into it, it'll graphically prompt the user for a specific thing, and then it'll print that thing to stdout. I use it to switch to named workspaces and to launch programs.
Anyways, yeah, dmenu and dwm just got it right. (Though I must admit I flirt with wmii these days). Every -nix'er owes it to him/herself to put 'exec dwm' into their .xinitrc for a few months. This analogy won't do it justice - but - the way your mind expands shifting over is comparable to the development mentality shift one gets when moving from procedural C to LISP or Smalltalk.
Spotlight is way better for file searching though and its integrations are really good, but Alfred workflows are definitely worth looking into.