There are a number of strategies, each with its own level of risk:
provide your salary requirement. Provide the employer with what the company wants, but realize that you run a strong risk of being screened out if you are too far above or below the range the employer has in mind for the position.
Ask for a wide salary range. Even with some basic research, you should be able to determine a salary range for the position. As long as part of your range overlaps with the employer's range, you should be okay. But what if your highest amount matches their lowest amount? Yup, you will be stuck at the bottom of their pay scale. But, assuming you give a range that is acceptable to you, you should be okay. It may be better to state something like, "a salary in the mid $40's."
state that you expect competitive or fair compensation. Put the ball back in the employer's court by informing the company in your cover letter that you expect a competitive salary. The danger? If the employer doesn't offer a competitive salary -- or is a stickler for having an actual salary request -- you've eliminated yourself from being considered for the position.
Express your salary flexibility. Similar to the last strategy, simply state in your cover letter that you are flexible about salary. The danger is again not providing an actual salary request -- and that alone could eliminate you from consideration for the position.
state that you would prefer to discuss salary in an interview, but make sure to add that you don't think salary will be a problem. The danger is again not providing an actual salary request -- and that alone could eliminate you from consideration for the position.
Give your salary history. Ignore the request for a specific amount and simply show your salary history with the idea that your next job offer should be reasonably higher than your current salary. The problem here is that you have not provided the information the employer seeks, and you may be eliminated.
Ignore the salary request. Many people believe that employers have no right making a salary request so early in the process and simply ignore the request. The most likely occurrence? If you ignore the request, your application will most likely be ignored as well.