IMSLP:API

You can access a list of composers and works present on IMSLP using the following two URLs:

List of people (composers, performers, editors, etc.): http://imslp.org/imslpscripts/API.ISCR.php?account=worklist/disclaimer=accepted/sort=id/type=1/start=0/retformat=<pretty|json|php|wddx>
List of works: http://imslp.org/imslpscripts/API.ISCR.php?account=worklist/disclaimer=accepted/sort=id/type=2/start=0/retformat=<pretty|json|php|wddx>

You can page through the list by changing the start value (this is the entry # that the results start from).