You may be hard pressed to find places that accept donations of used pillows for sanitary reasons. However, local animal rescue or wildlife shelters might be interested (or you could turn them into pet beds and donate those). Some animal shelters will not take pillows as it would require too much effort to repeatedly wash them, and each place has it's own set of rules and needs, so please check to find out.

You could also give them away via a classified ad or material exchange site to someone who could get a little more use from them.

Foam pillows might be best taken to mattress or foam recyclers.

Look here for more ideas http://earth911.com/home-garden/7-ways-to-reuse-and-recycle-old-pillows/ 

Some thrift stores will accept them for fiber recycling (call ahead to find out)

If your pillows are feather or down, they can be emptied into a compost bin and the outer cover recycled with textiles.