The Munter Hitch
The Munter hitch is reliable, assuming you know how to set it up correctly. You can use either one locking or two opposing carabiners. Make two bights in the rappel rope, like a clove hitch, and fold one over the other. Clip the loops through the carabiner(s) which are clipped to your harness (preferrably belay loop, gear loop will not work!). Then start heading down. It will kink your rope, but you'll get over it.
The Carbiner Brake
The Carbiner Brake can be done with either six carabiners or one large locking and four regular carabiners (the large locking connecting to your harness). When using two carabiners, ALWAYS reverse the gates. These first two will keep the rope from running against your harness, however they can be eliminated in an emergency if you only have four. Then clip two opposing ovals (or Ds, although ovals are best) to the two on your harness. Put a bight of the double ropes through these two. Clip the last two ovals across these two and under the bights so they rope runs over the backs of the pair.