Fibonacci Hashing: The Optimization that the World Forgot (or: a Better Alternative to Integer Modulo)
David MacKay has put the textbook he wrote online for everyone to download in a variety of formats. If you find it useful, consider buying a copy.
A free, online book on the C programming language. There is also a downloadable .pdf file of the contents of the e-book so you don't have to try to archive the whole website.
A website about randomness, (pseudo-)random number generators, and cryptographic entropy. Contains discussions of these topics as well as some online RNGs to play with.
A list of tricks and methods for optimizing code written for the ATmel microcontrollers using GNU GCC.
A programming language and development environment for realtime audio synthesis and algorithmic composition of music.
A list of common algorithms in computer science, compiled at Wikipedia.
An online directory ('zoo') of all of the known quantum algorithms that have been devised so far, their operational parameters, and uses.
Lifewiki is /the/ wiki to visit if you're interested in Conway's Game of Life in particular, or cellular automata in general. You can get lost here for weeks, so take your time.
NuPIC is a client/server system for developing AI applications that use HTMs (hierarchical temporal memories) and machine learning to operate in specific problem domains.
A technical reference site that has lots of odd information, most of it PC related. Data formats, file extensions, datastructures and algorithms of sundry kinds and uses, hardware specs, microcontrollers, history, advice... there's a lot of stuff buried in here. If you need something you could do worse than check here first.
A site that offers many different algorithms, functions, and models as microservices that you can send data to via REST API and then receive results from. A Huginn agent has been created as a ruby gem already. An official Python module that presents the API natively exists, also. Attempts to be as language agnostic as possible.
Python module that implements the summarization of html and text using several different algorithms.