For example do you want the assoc or the nodes themselves, do you want deep listing, or do you only want nodes of certain types or with certain assocs.
The following two services are full of many methods that may be useful. Node Service FileFolderService
FileFolderService has a listDeepFolders method. It was (in my opinion) over hastily "deprecated". It does however work since imap is dependent upon it.
Deep listing is problematic due to the sheer number of records that could be returned. Not quite sure what the correct solution is here. At minimum it needs to have paging.
Please: +1 for a general getChild Method of the NodeService which supports paging. FileFolderService is tied to cm:content etc. Not usable for archiveStore or version2Store e.g.