Some of the more popular destinations for transferring money are Mexico, India, Philippines, and the Latin areas. Many online money transfer services serve a niche market, usually because they have a strong presence in one of the countries.
Money transfer companies like Western Union and Money Gram are the largest and most used since they've been around the longest. They have the most physical locations worldwide. These money transfer services are highly visible in retail outlets along with offering an online option.
The newer money transfer companies offer lower fees and flexibility. The recipients can receive their money by home delivery, bank account, or at one of their partner locations.
People transferring money regularly is the reason more of these companies popping up. There are a lot of people working in foreign lands that regularly send money home. The United States, for instance, has a huge immigrant population that regularly transfers money abroad.
This is ideal solution for non US residents. It is good for worldwide money transfers, online payments, or funding another bank account.