Sources

If you're looking for places to pull either file format information, or to verify stuff you've found, or to go that extra mile to track down variations, here's some similar endeavors and items.

List of Places Keeping Track of Formats
The following resources are no longer available:

Emulation

 * http://nonmess.retrogames.com/ - Emulator listing for various computer formats, including MESS and single-machine emulators.
 * The Emulation Framework is software developed by the international KEEP project, co-funded by the European Union's 7th Framework Programme.

Books

 * Compressed Image File Formats: JPEG, PNG, GIF, XBM, BMP by John Miano (1999)
 * Encyclopedia of Graphics File Formats by James D. Murray and William VanRyper (1994, 1996) Copy Acquired! Refer to the main article.
 * Graphics File Formats by David C. Kay and John R. Levine (1994)
 * Graphics File Formats: Reference and Guide by C. Wayne Brown, Barry J. Shepherd (1994)
 * File Formats for Popular Personal Computer Software: A Programmer's Reference (Self-teaching Guides) by Jeff Walden (1986) Copy Acquired!
 * File Formats on the Internet: A Guide for PC Users by Allison B. Zhang (1996) Copy Acquired!
 * 3D Graphics File Formats: A Programmer's Reference by Keith Rule (1996)
 * More File Formats for Popular PC Software: A Programmer's Reference by Jeff Walden (1987) Copy Acquired!
 * Lotus File Formats for 1-2-3 Symphony & Jazz: File Structure Descriptions for Developers from Lotus, Inc. (1986)
 * Inside Windows File Formats by Tom Swan (Nov 1993)
 * Internet File Formats: Your Complete Resource for Sending, Receiving, and Using Internet Files by Tim Kientzle (Oct 15, 1995)
 * File Formats for Popular PC Software by Jeff Walden (Nov 1992)
 * PC File Formats and Conversions/Book and Disk (Developers Series) by Ralf Kussmann (Mar 1990)
 * Windows Undocumented File Formats; Working Inside 16- and 32- bit Windows by Pete Davis (Jan 23, 1997)
 * Graphics File Formats: The Complete Reference by John R. Levine and David C. Kay (May 1992)
 * Using Pcx Graphics Files: The Programmer's Definitive Guide to Pcx File Formats by Roger T. Stevens (Apr 1, 1996)
 * The File Formats Handbook by Gunter Born (Sep 1995)
 * X Window System File Formats and Application Conventions (X11R4) by The Open Group (Jul 17, 1991)
 * Guidelines on the Production and Preservation of Digital Audio Objects by IASA (2009)
 * Android Forensics: Investigation, Analysis and Mobile Security for Google Android - Andrew Hoog - contains info on the Android file structure and how to obtain data from a locked phone, usually of a dead person, or a poor guy who forgot his password.

Other Useful Materials and Services

 * http://www.nsrl.nist.gov/ National Software Reference Library (see also http://blogs.loc.gov/digitalpreservation/2012/05/life-saving-the-national-software-reference-library/)
 * http://www.openplanetsfoundation.org/software/fido Format Identification for Digital Objects
 * https://github.com/usnationalarchives/File-Analyzer File Analyzer
 * https://sk1project.net/modules.php?name=Products&product=uniconvertor UniConvertor is a universal vector graphics translator. It is a command line tool which uses sK1 object model to convert one format to another
 * http://www.textfiles.com/programming/FORMATS/
 * http://wiki.opf-labs.org/display/SPR/Digital+Preservation+Tools Wiki list of digital preservation tool lists
 * http://wiki.opf-labs.org/display/REQ/Digital+Preservation+and+Data+Curation+Requirements+and+Solutions Digital Preservation and Data Curation Requirements and Solutions. Not classified by formats, but by datasets, issues and solutions.
 * http://fileformats.wordpress.com/ - The File Formats Blog
 * http://www.archive.org/details/cdbbsarchive - The Internet Archive has over 1,500 CD-ROMs loaded with shareware, and with that comes converters, documentation and other vital works related to file formats.
 * Crowd sourced Representation Information for Supporting Preservation (cRIsp)
 * National Software Reference Library
 * Linked Data URIs for MIME Types
 * http://darwinsys.com/file/ UNIX file(1) format guessing utility
 * http://www.filesignatures.net/ Online database of file signatures (magic numbers)
 * http://www.garykessler.net/library/file_sigs.html List of file signatures (magic numbers)
 * Data Formats from Paul Bourke Useful information on older formats. Categories include Geometric (e.g., 3-D), Audio, and Image.
 * Graphics File Formats page from Martin Reddy Useful information on older formats. Categories are: 2-D and 3-D, with supplementary resources.
 * LibAV Sample Files collection, over 50GB
 * http://www.corel.com/content/pdf/wpx4/corel-wordperfect-office-X4-reviewers-guide.pdf Corel WordPerfect Office Reviewers Guide, Appendix A gives useful overview of old Office formats + their typical file extensions.
 * http://documentation.statsoft.com/STATISTICAHelp.aspx?path=common/CommonMenus/CompatibleDocumentTypes Some info on formats of / compatible with Statsoft Statistica
 * http://web-beta.archive.org/web/20100210224635/http://medlem.spray.se/converters Loads of DOS / Windows conversion programs - this appears to be the most recent grab held by the Internet Archive
 * https://github.com/kreativekorp/ksfl Project to read/write various container formats
 * http://www.kreativekorp.com/swdownload/wildfire/HC%20FILE%20FORMAT%202010.TXT Description of the HyperCard stack file format
 * Media Archeology Lab
 * Bitsavers document library of DEC manuals
 * Document Liberation Project
 * Unusual sources of file format signatures
 * The Dead Media Project
 * Advice on File Formats for the Creation of Digital Records (Archives New Zealand)
 * An introduction to using the command line interface to work with files and directories
 * DigiPres Commons Community-owned digital preservation resources
 * POWRR Tool Grid
 * Falstaff: online file identification utility
 * BitCurator access tools
 * Document Liberation Project projects
 * Open LossLess in STanDards (GitHub)
 * http://www.manmrk.net/tutorials/compress/index.htm A large collection of 1990s compression software