One of the easiest ways to get publicity for your agencies is to write an Op-Ed piece for a local, regional, or national publication. Sit down with a calendar and identify four dates that lend themselves naturally to your work (for example, an organization that works with children could probably write a piece for the holidays, one for the back to school season, one for the US observance of children's day, and one for Mother's Day) and beginning planning opinion pieces around those themes. Throughout the year, also keep your eyes open for items in the news (the example organization from above could have used the numerous toy recalls this year) that align with your organization's work.
Once you've started to craft your opinion pieces, think hard about what kinds of publications would be good targets for your initial pitch. Start locally, and then branch out from there. I'm always an advocate of starting small - but definitely don't limit yourself. Make a list of 10 - 20 publications with audiences that wold be interested in what you have to say, and then do your homework. Contact them to find out how to submit your Op-Ed piece properly. Read the publication's opinion section for several consecutive months to understand what kind of tone of voice their editor prefers.
And last but not least - edit, proofread, and edit again. Before you submit your piece, be completely sure that it's well written, factual, clear and concise. Don't trust your own eyes - ask for help.
It's worth the effort. Well placed Op-Ed pieces are a great way to get free publicity for your agency.