This is not really code, but close enough: my version of a modern C Coding Guideline.
The page about Optimisations of AVR programs using avr-gcc explains how to get smaller code on an AVR 8 bit microprocessor, using avr-gcc or WinAVR.
The German Einführung in sed (a German introduction to sed, the stream editor) is now quite mature and also well visited. English speakers might find the shell tips useful as well as the sed intro. These pages are supplemented by some notes about Regular Expressions.
The old article about Virtual domains with Exim + Courier-IMAP + MySQL is still visited frequently. My 2 cents regarding a iptables firewall show how to deal with ssh port knocking. The Sieve tutorial, the server-side mail filtering language, is interesting for people who like to access their mails over IMAP using different mail clients.
I have written a few short texts on Subversion Backup, Tuning Subversion over HTTP, renaming the author in a SVN log and a git svn cheat sheet partly because I needed those information repeatedly and partly because some of the information was hard to find.