A First Course in Pharmacokinetics and Biopharmaceutics: The basics of kinetics. Starts with mathematical equations and relations and leads you to the related applications in medical and pharmaceutical applications. The best theoretical approach to the theme I know.
Clinical Pharmacology is a useful section of the Merck Manuals. It contains 9 sub-chapters dealing with basics as drug input and disposition, pharmacokinetics, pharmacodynamics and drug toxicity as well as drug monitoring or drug therapy in the elderly.
The WFSA Update in Anaesthesia section on Pharmacology has just about everything you need to know.
Context Sensitive Decrement Times: This site explains how the nature of a drug and the duration of an infusion influences the offset of the drug effect. Examples include narcotics and general anaesthetic agents.
Pharmacokinetic and pharmacodynamic resources: This page provides a link to the PharmPK-mailing list with links to other pharmacology related sites.
PK Equations provides pharmacological constants and calculus.
Virtual Pharmacy Center - Martindale's Health Science Center: A very comprehensive collection of links for pharmacists and chemists primarily.
The Periodic Table of the Elements (WebElements) with atomic data.