Regular Websites
The National Radio Astronomy Observatory answers all the questions you can think about regarding data formats. - FAQs about Data Formats
http://www.cv.nrao.edu/fits/traffic/scidataformats/faq.html
Here you'll find a collection of file extensions; many linked to the programs that created the files. - FILExt
http://filext.com
If you have to deal with pdf formats, then the pdf converter may interest you. Produced by leading software company Mystik Media, it can convert almost any file type to pdf, or convert pdf files to almost any other file format. - PDF Converter
http://www.mystikmedia.com/pdf_converter.htm
PDF2XL is a PDF to Excel converter which includes a conversion preview view and multiple page conversion support - PDF to Excel Converter
http://www.cogniview.com/pdf2xl.php
Covers Microsoft BizTalk, webservices and all uses of XML in many languages supporting XML with XML tutorials, references, tools, XML developer resources, XML discussion forums and XML blogs. - TopXML
http://www.topxml.com/
University of Western Australia
Paul Bourke of the University of Western Australia provides an extensive list of all the various data formats. - University of Western Australia
http://local.wasp.uwa.edu.au/~pbourke/dataformats/
Checks your web pages to see if they are W3C standards compliant. Can either check live pages or upload pages that aren't live to be checked. - W3 Validator
http://validator.w3.org/
Comprehensive resource on data formats, including a full list of all formats covered, graphic files, movies, databases and more. - Wot Is It
http://www.wotsit.org/