On this page I'll throw out some useful links on the web that I consult from time to time. Most are at least somewhat related to the subject of antenna theory.
The Fourier Transform .com - Fourier Transforms arise a fair amount in antenna theory, as the radiation from apertures in the far field is the Fourier Transform of the aperture distribution. Also, this subject is just plane cool, so it is worth knowing about. And the math on this site isn't too bad. It includes a clickable-for-derivation table of Fourier Transforms.
Maxwell's Equations - Most people don't know anything about Maxwell's Equations, and most engineers and physicists could write them down for you, but will be taken aback if you ask them what they mean. So this page is all about explaining all the math and the general concept of the equations, including why they matter and why we care.
The Blog of Jeremy Blum - This is the website of the guy from Cornell who programmed his cap to be controllable via the web, which was covered by Engadget, Wired, etc. It turns out he's a guy who knows a thing or two about engineering, and in particular a bit of an Arduino microncontroller expert. His blog often discusses interesting do-it-yourself projects that you can learn from, or at least be entertained by.
Why Is The Sky Blue? - This site examines why the sky is blue. There's actually a fair amount of thought and electromagnetics involved in understanding the answer. Hence, this is a great question for antenna engineers to be able to answer.
When Does the Time Change? - This site isn't directly related to antenna theory, but who can remember when to set their clock back for daylight savings time?
Where Are the Hamptons? - This site also isn't directly related to antenna theory, but I bet you won't leave it not knowing where the Hamptons are. Actually, that entire site is about answering simple google queries that begin with "Where are the ___".