This is a small list of casting notices for actors, and job listings for musicians, technicians, directors, etc. If you click on any of the sub-categories, however, you'll find that they're further divided to the point where the nomenclature makes sense. The database is searchable by name, production or year. These lists of links are valid but short, with a preponderance of dance related sites. You'll also see mention of the Playbill On-Line Club.
Membership is free, and is well worth the price.
Other than the few niggling complaints mentioned above, there are few major inconveniences. Altogether this is an excellent site, both readable as an e-magazine and searchable as a theatrical information database. I think you'll find any time spent at Playbill On-Line to be worthwhile. Used under License.