Prior to the invention of transistors, digital circuits were composed of vacuum tubes, which had many disadvantages. They were much larger, required more energy, dissipated more heat, and were more prone to failures. It's safe to say that without the invention of transistors, computing as we know it today would not be possible.

GlobalSpec.com: Transistors - Provides database of suppliers for transistors. Includes catalogs, technical information, and supplier contact information.

Mister Transistor
Hosted by a collector of transistors, this site offers historical information, collector information, an image gallery, and links to electronics and transistor related sites.

Yahoo!'s transistor manufacturers page
Yahoo!'s directory of transistor manufacturers.

Microprocessor Comparison Chart
A cut-to-the-chase guide that compares and contrasts popular processing chips.