The only sure-fire method of beating the wheel that I ever heard of was done by some MIT grad students who clocked a number of wheels in Vegas and found some that were slightly out of balance, giving them a slight edge. Over time, they made money.
No bias is needed. You can clock any wheel, even a perfect one. Once the ball is in the wheel most casinos allow you to still place bets. When you know where the ball enters the wheel, how fast the wheel is spinning and how fast the ball is going then suddenly it is not anymore an even chance for the ball to fall into any one of the slots. Using this information you can derive a sector of slots into which the ball is more likely to fall. The key is then to place quickly the appropriate bets to cover this sector on the wheel. As you might imagine, you need a computer to figure this out in a split second and then you need a quick hand or a team to place the bets.