Friends and Sisters
The standard scenario when it comes to bridal showers is the bride's friends and sisters pay for it. A shower is thrown for the bride by her sisters or friends (specifically managed by the maid of honor). If the bride has no sisters, she can ask the maid of honor for help, and the maid of honor can go to the bride's maids for financial assistance for the shower.
The bride's parents can pay. A bride-to-be can ask her parents to pick up the bill for the hall and the food. They can also be asked to assist with the cake, decorations and gifts. In most situations, the bride's parents do not pay for the hall as they are traditionally considered to pay for the reception.
The couple-to-be can pick up the bill. The bride and groom can pool together and pay for the shower if her friends, sisters or parents do not offer or cannot pay for the shower. This is a newer concept that allows for the couple to have greater say in the shower's logistics.