Australian-developed Nitro Reader 3 remains our favourite tool for working with PDFs: it's free, it lets you edit and sign PDF files, and it works far better and less intrusively than Adobe's Reader. Version 3 has just been released and adds several cool features, including auto-saving when you edit files and smart alignment of text when you are filling in scanned forms.
Other enhancements include improved annotation compression, meaning that files with lots of annotation save with much smaller file sizes, and support for an additional 15 languages. Even if you don't need those options, the ability to easily edit any PDF file and automatically add your own signature remains a huge time-saver, and reason enough to swap to Nitro.
Nitro Reader 3.0 is a free download for Windows.