Many employers will pay for your master's degree if it seems like it will further your performance in their given field, thus making you a better employee and benefiting both parties. Often, employers will ask for a certain reciprocal agreement, such as agreeing to stay on for a given amount of time, in return.
Big consulting firms, banks, stockbrokers, and financial analysis firms are all examples of companies that may offer programs to pay for your Master of Business Administration. Even if there isn't a program in place at a business, you may be able to make a case for yourself after a year or so of working there by telling them an MBA will help your work efforts.
Any research firm or company that deals in scientific development will likely offer a program to pay for a master's degree in your specialized field. You may not be able to get a higher level job at companies like these without a master's degree, but many people start in admin or other positions and then work their way up. If a company likes to promote from within, which you can find out in the interview, they would likely pay for a degree in a higher field.
Publishing firms will often pay for a Master of Fine Arts. Random House, for example, has a track for professionals to earn their MFAs after a set amount of time, to be decided by your supervisor, has passed. Also, certain universities will pay for master's degrees in varying academic subjects.
Depending on the type of job you are working, you can probably make a case for a master's degree to your employer. Libraries often pay for employees to earn master's of library sciences, for example. Many schools will pay for a master's degree in education for a teacher, who must earn the degree within five years. Check with the human resources department or your supervisor for options that will further you in your chosen field.