External File-based Data Source Options for a PivotTable

What options are there to use as a data source for a Pivot Table?

Here are the criteria:

1. Must be a file (or files) located on disk.
2. When I press Refresh All, it should refresh all pivot tables from the datasource (which may have been changed entirely).
3. I can define calculated fields in the datasource. (For fields that need to be summarized with a weighted-average).
4. Fast, efficient. The datasource may have a hundreds of columns and hundreds of thousands of rows.