WinZip

Like the aforementioned Adobe Acrobat Reader, WinZip may not be flashy, but it's one of those programs you won't want to go without for very long. Not only does the program prove capable of transforming large batches of files into a much smaller archive, it also boasts extras such as encryption and virus checking. Most notably, WinZip's ease of use can't be beat; even Luddites will quickly get up to speed, thanks to the inclusion of multiple wizards.