I like the look of the big-fish/little-fish set-ups...but they have to be done right. The big fish must be BIG...and the little fish must be very little, and also fairly numerous.
HarleyK
has the perfect set-up.
Three-inch Tiger Barbs, along with wolves in the 5-to-10 inch range? That will just look like a very expensive feeding frenzy...which, coincidentally, is what the above example turned into.
I had success in the past with a large Giant Gourami (15-ish inches) living with a colony of guppies; he never paid them the slightest attention, but he never tried to eat any other fish of any size so that was an easy one. I also recall that the King of DIY had a large tank containing a single large Asian Arowana and a large number of small tetras...neons, I think? That set-up, like the wolf tank belonging to
HarleyK
, relied upon the size disparity being so great that the little guys were simply beneath the notice of the big predator.