Although in Beta, Nitro PDF reader is quite a competitor to Adobe Reader. And more importantly its Free
One of the main features is the UI, it is the Microsoft® Office®-style Ribbon interface. Tasks and tools are separated into tabs, grouped by functionality, and represented graphically with easy-to-understand text labels, providing an immediately familiar user interface that won’t leave you searching for help.
Work with Multiple files at the same time, using the Tab system.
You can preview pdf files in Windows Explorer using Nitro PDF reader too.
Nitro PDF Reader is the only Free PDF reader which allows you to create pdf files from almost 300 file types.
Also, you can extract text/images from pdf files, which is pretty cool.
These are just the major features, view a full list of features here.
All in all, a good package, you can download it from here for Windows 7/Vista/XP both 32 Bit and 64 Bit available here. (24 Mb)