2 Answers

Hi Mr/Ms_____, my name is _________, could I have a few minutes of your time? I am  looking for donations to help support ____________ . __________ is a non profit organization and depends on the generous support of others in order to operate fully. Explain a little about the organization and what it does to help whatever it's cause is. Give them the option of what they would like to donate or a small list of what you think would work best. Make sure you let them know their charitable donation can be written off on their next years taxes. 

<font face="mceinline">In addition to Colleen's answer, if you can offer them some free advertising by having a poster of contributors, or a program which lists their names, that is appealing.  Complimenting the company on its product or service is nice....it implies you know them and are not just looking for a handout. If you are a patron, even better.  Also, sometimes you can ask what THEY would like to donate instead of requiesting something in particular.
I guess what I am saying is to personalize and promote.  </font>