Preview

Apple's Preview application (which is included as part of Mac OS X Tiger) is best known as a PDF viewer and a Macintosh alternative to Adobe Reader.

You can bookmark PDF pages, add comments, fill out PDF forms, and copy text selections from within the file. This software, however, is also a capable image viewer for file formats such as JPEG, GIF, PNG, PSD, PICT, TIFF, and others, and it even allows you to edit those images. Preview can capture screenshots by selecting the Grab utility under its File menu. Many Mac users prefer using Preview over Adobe Reader because it takes less time to open and renders file pages very quickly.