UEFA competition bans
The primary point of any sport is to compete and win. It's why there is such dedication in training, and honing and perfecting skills. Sport is ultimately about being the best, and using everything required to succeed. To prove that one is the best, one needs to compete at the highest echelon. For European clubs, that is UEFA Champions League and UEFA Europa League.
If the oppurtunity to compete at the highest level is denied, it could be an effective sanction for any club with excessive racist incidents. This again will be a blow for revenue and exposure, forcing clubs to improve their stance or be left out.
The amount of money and exposure generated from being in UEFA's European competitions are ever-increasing - and it would be a severe hit if any club is barred from participating in them for this reason alone.
Top players wouldn't want to join clubs that aren't at the highest levels. So it should, in theory at the least, spur clubs into taking positive action.