Measure-theoretic probability: Why it should be learnt and how to get started. The clickable chart of distribution relationships. Just two of the interesting and informative probability resources I've learned about, along with countless other tidbits of information, from statistician John D. Cook's blog and his probability fact-of-the-day Twitter feed ProbFact. John also has daily tip and fact Twitter feeds for Windows keyboard shortcuts, regular expressions, TeX and LaTeX, algebra and number theory, topology and geometry, real and complex analysis, and beginning tomorrow, computer science and statistics.
Russel Cox, one of the people behind Google's new programming language Go, has written a three part series on regular expressions. It's a nice mix of computer science theory, programming, and history: Regular Expression Matching Can Be Simple And Fast, Regular Expression Matching: the Virtual Machine Approach, and Regular Expression Matching in the Wild.
Regex Dictionary - for those times when you want a web-based dictionary you can search with regular expressions.
Every time you attempt to parse HTML with regular expressions, the unholy child weeps the blood of virgins, and Russian hackers pwn your webapp. Parsing HTML with regex summons tainted souls into the realm of the living. HTML and regex go together like love, marriage, and ritual infanticide. The <center> cannot hold it is too late. The force of regex and HTML together in the same conceptual space will destroy your mind like so much watery putty.