(See also Application Notes on this site)
Circuit Cellar, May 1998: Practical Analog Design
Understanding Op-Amp Specifications (Texas Instruments White Paper)
The Monolithic Op-Amp: A Tutorial Study (National AN-A)
Basic Feedback Theory (Phillips AN-166)
A Basic Introduction to Filters - Active, Passive and Switched-Capacitor (National AN-779)
On Designing High-Speed Active Filters (National OA-26)
An Introduction to the Sampling Theorem (National AN-236)
Sinewave Generation Techniques (National AN-263)
A Tutorial on Applying Op-Amps to RF Applications (National OA-11)
Data Communications...