I've had all kinds of fish tanks, freshwater tropical, saltwater, liverock.  But my favorite was when I collected the fish myself from local lakes.  
I've had two different native tanks.  The first had two bluegill, two crappie, and a largemouth bass.  I put a dozen minnows in the tank that I bought from a local bait store, boy what a feeding frenzy that was!  The second contained six pumpkinseeds (a very colorful type of sunfish).  I had a sand substrate and live plants I grew from bulbs.  Was a very pretty tank.  However, once the pumpkinseeds started trying to breed, they got too aggressive, so I released back where I caught them.