The Benzinga delayed price quotes API delivers 15 minute delayed price quotes for the most popular American exchanges. Data points include open, low & high (including 52-week), close, daily volume, and various % change numbers are available in the API. For a full list of fields view the documentation.
An expansive historical database is also available through the API. The following table breaks down the availability of pricing data at specific intervals.
Pull-based XML/JSON API