KOReader is a document viewer for E Ink devices. It supports PDF, DjVu, XPS, CBT, CBZ, FB2, PDB, TXT, HTML, RTF, CHM, EPUB, DOC, MOBI, and ZIP files. It currently runs on Kindle, Kobo, PocketBook, Ubuntu Touch and Android devices.
Visual online tool for PDF document cropping / changing canvas size. You can crop the PDF to a selected area, adjust margin size or autocrop visible margins.
Skim is a PDF reader and note-taker for OS X. It is designed to help you read and annotate scientific papers in PDF, but is also great for viewing any PDF file.