The following books discuss various issues related to resource monitoring, and are good resources for Red Hat Enterprise Linux system administrators:
The System Administrators Guide; Red Hat, Inc -- Includes a chapter on many of the resource monitoring tools described here.
Linux Performance Tuning and Capacity Planning by Jason R. Fink and Matthew D. Sherer; Sams -- Provides more in-depth overviews of the resource monitoring tools presented here, and includes others that might be appropriate for more specific resource monitoring needs.
Linux Administration Handbook by Evi Nemeth, Garth Snyder, and Trent R. Hein; Prentice Hall -- Provides a short chapter similar in scope to this book, but includes an interesting section on diagnosing a system that has suddenly slowed down.
Linux System Administration: A User's Guide by Marcel Gagne; Addison Wesley Professional -- Contains a small chapter on performance monitoring and tuning.