I've heard a variety of different methods for keeping your brown sugar de-clumped, and to be honest, I'm a bit wary of each one. Here's a breakdown of what the grapevine says about keeping your brown sugar fresh --- why not give it a shot and report back with your findings?:

According to ThriftyFun:
Store brown sugar you plan to save for later baking in an airtight container with a fresh slice of bread. The moisture in the bread will keep your sugar soft, moist, and ready-to-use. When the bread dries and hardens, simply replace it with a fresh slice. You can feed the old, dry one to the birds and squirrels.

From WiseGeek:
If your brown sugar is hard as a brick, you can restore it to a usable consistency by placing it in a tightly sealed container with an apple wedge for one to three days.

From WiseGeek:
You can purchase a terracotta disk at many kitchen supply stores that will keep your brown sugar free flowing.

Which sounds like the real deal to you? Any brown sugar tips you swear by?