From American FactFinder's Advanced Search page: you can download up to 10 tables in a comma-delimited format (.csv).
When viewing an individual table, you can choose to download it in comma-delimited (.csv), PDF, Microsoft Excel (.xls), or Rich Text Format (.rtf) formats. Downloads can be for either a single table or multiple tables.
Download Center helps you select and download large amounts of data. The download center steps you through selecting up to 40 tables for a set of geographies (all counties in the United States, all places in California, etc.).