Below is a list of websites I found useful or interesting:

Academics and Practice

Amit Patel's Homepage

• Amit Patel's homepage which gives various lessons and tips on game programming, AI, and algorithms

Red Blob Games

• Webpage by Amit Patel that delves further into game programming and applications of algorithms on games

Susskind's Online Physics Lectures

• Online video lectures by Dr. Susskind on various physics topics ranging from classical mechanics to quantum theory and general relativity

The Theoretical Minimum

• Website by Dr. Susskind in which he keeps all of his recorded lectures on physics. Official site of the one above

The Open Academy

• An online list of courses from various topics including engineering, science, and mathematics

Artificial Intelligence: A Modern Approach

• Webpage for the popular AI book of the same title. Has a code repository, errata, and other useful links.

Rosalind Bioinformatics

• A website that teaches bioinformatics through problem solving.

Project Euler

• A series of mathematical and computational problems for students to practice and learn

The New Boston

• A great page for learning how to program. Covers various languages such as C++, C#, Java, Python, and several others.

BetterExplained

• Useful site that explains various mathematical and other concepts quite simply

CodingBat

• Site for practicing Java and Python online. Compiler integrated within the site.

Google Code Jam

• Annual worldwide coding competition sponsored by Google. Has record of previous competition problems for practice.

Top Coder

• Site where several coding competitions are held throughout the year sponsored by various companies

Sixty Symbols

• Several videos explaining concepts in physics and astronomy

EDU - Youtube

• Youtube site with thousands of educational videos for various subjects

Scholarpedia

• A peer-reviewd open-acces encyclopedia where articles by experts from various fields are published. Similar to Wikipedia but much more in depth.

Open Culture

• A blog that contains links to various free educational material and media

Foolproof by Design

• A blog about video game and web design

The Feynman Lectures on Physics

• Famous lecture notes by Richard Feynman on the basics of physics

The Physics Hypertextbook

• Online physics textbook covering mechanics, electromagnetics, thermodynamics, and nuclear physics

Grad School

Applying to PhD Programs in Computer Science

• Offers great insight for applying to PhD programs in general

3 qualities of a successful PhD Student

• Gives great tips on how to be a successful PhD student

HOWTO: Get into grad school for science, engineering, math and computer science

• Tips on how to apply for grad school, in particular PhD programs

10 easy ways to fail a PhD

• Gives some basic reasons why many students don't succeed in PhD programs

PhD Program Flowchart

• An useful flowchart starting from applying to a PhD program to thesis defense

A Graduate School Survival Guide

• A survival guide for Computer Science graduate students from the perspective of a former student and professor

Grad School Admissions

• Blog from former MIT student about graduate admissions

Writing Recommendations

• Tips from MIT Admissions about effective recommendations

How to Write a Great Statement of Purpose

• Tipes on how to write a statement of purpose from an professor from the University of Northern Iowa

PhD Comics

• Good comics and videos about life as a PhD student and similar topics.

DJStrouse

• Site by DJStrouse about his application process to graduate school. Contains essays he wrote.

The PhD Grind

• A memoir during the PhD years

The Professor is In

• Blog about academia and tenure track

Sofware Development

Dark Flow

• A visual video game IDE that allows users to develop video games with drag & drop. Available in free and commercial versions.

jMonkey

• Java based open-source video game engine that uses Java OpenGL

Unity

• Video game engine based on C/C++. Available in free and commercial versions.

Python Programming

• Official site for the Python programming language

Portable Python

• Site for downloading a portable version of Python

Eclipse Foundation

• An open source IDE that supports C++, Java, Python, and several other programming languags.

GNU Octave

• An open source alternative for MATLAB used mainly for mathematical computations

Scilab

• Another open source alternative for MATLAB used for numerical computations

Code Project

• Online community for software developers to share code and knowledge for free.

GameDev.net

• Online community were developers share their knowledge and expertise through forums and short lessons. The site has a particular emphasis on game development.

Gamedev Tutorials

• Introductory tutorials on game development.

GameDev.com

• Game development forum with tutorials and information on various aspects of game development.

Mozilla Thimble

• Online editor to practice HTML, CSS, and Javascript through interactive graphics.

Travel

Worldpackers

• Opportunities to find jobs around the world in exchange for room & board. Jobs vary from receptionists and cooks to web developers and photographers.

Hostelworld

• Excellent resource to book hostels from around the world.

Odigo

• Itineraries, info on interesting locations, and blogs about Japan. Perfect for planning your trip to the land of the rising sun.

Nomadic Matt

• Great blog to plan trips around the world. Features all your standard locations like Thailand, France, Spain, and many others.

Warm Showers

• Free hospitality exchange community for cyclists around the world.

Couch Surfing

• Community to help you couchsurf anywhere in the world.

Earth Trekkers

• Great for planning family trips.

Tripadvisor

• Good place to research destinations through user reviews and book tours.

International School Services

• Job forum to look for teaching position in international schools around the globe. Not just English language teachers but any content in elementary, junior high or high school including math, computing, history, physical education, and so on.

Other

100,000 Stars

• Simulation by Google of the 100,000 closest starts to our solar system

The Scale of the Universe 2

• Shows the scale of various objects in the universe from the microscopic to the entire universe.

Workshop - Chrome Experiments

• Site were various projects under development for Google Chrome are posted

Distance to Mars

• Website that shows the distance from Earth to Mars in pixels.

The Last Question

• Interesting short story by Isaac Asimov

The Fallacy Files: Taxonomy of Logical Fallacies

• A list and explanations of various types of logical fallacies along with diagrams.

Welcome To Science

• Interesting comic about science

An Astronaut's Advice

• Another interesting comic

Open Source Ecology

• Site dedicated to promoting open source hardware for the basics of civlization. Includes schematics, models, materials, and cost estimates to make objects such as tractors and well diggers.

Bob Sutor

• Dr. Robert Sutor's Blog and personal website. Has various interesting topics.

50 years of exploration

• Interesting picture depicting how many space missions have been made in the past 50 years.

NeuroLogica

• Neurologist's blog about neuroscience, skepticism, and critical thinking.