To let a user pick from a list of existing filters, use the $filters and $myfilters keyword. This keyword supports query parameters StartsWith, Skip, and Take.
For example:
http://restapi.lucity.net/gbaMS/Work/WorkOrders.svc/$myfilters
http://restapi.lucity.net/gbaMS/Work/WorkOrders.svc/$filters
http://restapi.lucity.net/gbaMS/Work/WorkOrders.svc/$myfilters/$count
http://restapi.lucity.net/gbaMS/Work/WorkOrders.svc/$myfilters/$count?StartsWith=A
http://restapi.lucity.net/gbaMS/Work/WorkOrders.svc/$myfilters?StartsWith=A