Microsoft ISA Server

Collective Software
Filters for ISA Server 2004 including single sign-on, HTTP to HTTPS redirects, altering URL paths, terms-of-service screens, log enhancements. Free evaluations are provided.
http://www.collectivesoftware.com

GFI DownloadSecurity
Addon for ISA Server which scans files downloaded by users for viruses and trojans, and allows network administrators to specify what file types are allowed through.
http://www.gfi.com/dsec/

Introduction to ISA Server 2000 by Larry Hunt
Step by step tutorial on how to install and configure ISA Server 2000, ICS, domain controller and DHCP.
http://larryhuntjr.com

ISA Server Tools Repository
A collection of free tools and scripts for Microsoft ISA Server. Includes scripts to protect against malware, configure protocols, and workaround bugs.
http://www.isatools.org/

Microsoft Technet
Technical resources to help plan, deploy and maintain ISA server installations.
http://www.microsoft.com/technet/prodtechnol/isa/default.mspx

Proxy Log Analyzer
Software for extracting and analyzing data from MS Proxy Server and ISA server log files. Sample report files and ordering information.
http://www.mechanicalminds.com/software/pla/