Foxit Reader is a fast, free, lightweight alternative to Adobe Reader for opening and displaying PDF files. It's also feature-packed, though it lacks the print-to-PDF and conversion capabilities of fellow freebie Nitro PDF Reader.
I've been using Foxit Reader since back in the day... The day when Adobe Reader had become a fat slob of a program that took forever to boot and load files. Adobe has improved greatly, but so has Foxit Reader. The latest version has a new look that mimics Microsoft Office 2007/2010 somewhat, and adds support for XML Form Architecture form filling, as well as Microsoft Active Directory Rights Management service. It also offers the ability to capture text, copy and paste it, though there's no wholesale export.
I now use Nitro PDF Reader, because it offers print-to-PDF and creation abilities for free, but I'll be working Foxit back into the rotation simply because of its speed. It's perhaps twice as fast as Nitro at opening, and especially searching files, and time is money.
Note: Foxit Reader 5 will install a toolbar and change your default search engine to Ask if you don't disable these options.