Sorry, but these links are badly in need of reviewing and updating. I hope to get around to it soon.
Amamogawa Click on ‘EMC/EMI’, then ‘Java Applets’
University of Missouri-Rolla EMC Laboratory
Hyperlynx (product demonstrator)
UltraCAD Design, Inc.
Printed circuit board trace impedances (PCB transmission lines)
University of Missouri-Rolla EMC Laboratory Click on ‘PCB Trace Impedance Calculator’
Applied Wave Research
UltraCAD Design, Inc.'s Calculators Click on the appropriate link
Shielding effectiveness of enclosures
York University
Amamogawa Click on ‘EMC/EMI’, then ‘Java Applets’, then ‘Shielding Effectiveness’
Loop inductance
IN3OTD
University of Missouri-Rolla EMC Laboratory Click on ‘Inductance Calculator’