Downloadable file links are accompanied by icons to indicate the type of the file:
Archives ... typically "zip" files, but any file whose name ends in .7z, .ace, .arj, .bz2, .cab, .iso, .jar, .gz, .lzh, .tar, .tar.gz, .tgz, .rar, .uue, .z, .zip
Audio ... files whose names end in .mid, .midi, .mod, .mdz, .s3m, .s3z, .it, .itz, .xm, .xmz, .mp4, .mp3, .mp2, .mp1, .aac, .apl, .vlb, .m4a, .m4b, .ogg, .aiff, .au, .voc, .wav, .wma
Documents ... typically Microsoft Word or Adobe Portable Document Format ... files whose names end in .doc, .pdf, .rtf
Hypertext files ... files whose names end in .htm, .html, .rhtml or .xhtml
Images ... files whose names end in .gif, .jpg, .png
Microsoft Powerpoint files ... files whose names end in .ppt
Microsoft Excel files ... files whose names end in .xls
Plain text files ... files whose names end in .txt
Videos ... files whose names end in .asf, .avi, .mov, .mp4, .mpg, .mpeg, .rm, .wmv
Anything else ... files whose names do not have one of the above endings.
