Personally I recomend d20 or Percentile since the odds are easier to calculate than multiple d6s. If you must use d6s I recomend a system like Risk or Warhammer where each indivual dice is determined as a sucess or failure on its own. 2d6 is O.K. since the distrubution is well known, 3d6 distrubutions are also not too hard to find. Be wary of systems *cough* tunnels and trolls* which compare sums of 2d6 to 3d6 or 4d6, as 2d6 has very low chance of beating 3d6. 2d6 second highest roll 11 is just barely above the average value 10.5 of 3d6. Increasing the number of dice just makes it worse, since the more dice you roll the more likely you are to come up with a value near the average. If you are just looking for which dice are the coolest looking check out the on-line site of the Worlds Largest Dice collection here