I admit it, I'm a geek. I like Free Software, consider the [Hacker] Jargon File as a world cultural heritage, I find the asr-manpages, Everybody loves Eric and xkcd funny and write this page in an editor that is older than me.
Who works with Linux or BSD, will sooner or later find the need to learn to use the shell properly. Advanced bash Scripting is a good introduction to command line programming with the most popular shell on UNIX. Heiner Steven's shelldorado.com is a rich source for shell tips.
The best English-German online dictionary is probably LEO. The funniest online translator is definitely Babelfish.
The NCRLC Russian Webcasts by the George Washington University is a excellent complement to a Russian course. This Webcast of recent news in Russian language is completed with a list of new words and a full transcript of the text.
The O'Reilly Network features a list of articles on web development, open source development, open and emerging technologies. Highly recommendet.
I like smart algorithms like the ones described on Bit Twiddling Hacks or on the site of the excellent book Hacker's Delight.
Technical documentation is in my opinion best written in DocBook.org. A DocBook document is made of one or more XML file(s) which get processed by an XSLT processor and turned into HTML, PDF and many other formats. The language itself is described in the two online books DocBook: The Definitive Guide and DocBook XSL: The Complete Guide. The Docbook Frequently Asked Questions are a good source of information that don't get answered in the above books.
The Documentation Style Guide for OpenSolaris contains valuable tips on how to format the documentation and on how to (or not to) write the text.
The Curious Inventor Guides are some well made short introductions to technical stuff. My favourite is the one about soldering. I like the following companies to make PCBs: Olimex, Myro PCB, PCB Cart, Batch PCB.