Here are some organizations in and around Austin that are always looking for some help. 

Save Texas Cemeteries - This is a non profit group that has taken on the job of documenting and protecting cemeteries across the state. An opportunity for an Eagle Project is documenting and surveying a cemetery.  http://www.rootsweb.com/~cemetery/eagle.html

This is a list of some ideas that are not specific to any location – might give you some ideas