Computers and electronics
Types of PCs
Buying new PCs
This is the minimum hassle approach.
A large premium is paid for state of the art machines, whereas the cheapest computers are closest to being obsolete. The most value for money in terms of dollars/"computing miles" is in the mid-price range, which has stayed at roughly $700-$800 for about a decade (note that this price does not include monitor, etc.). A computer purchased for this price will typically be able to run any and all software for 3-4 years without suffering from poor performance. As performance gains have flattened out over the past few years, this price point will likely become more and more efficient.
Since hardware development tends to lead software development, programmers have few incentives towards making their programs memory-efficient. The first thing a computer runs out of is memory, so maxing out the memory (RAM) is typically the easiest way to increase performance. It's also one of the few ways you can manually upgrade a laptop. For office work, a modern CPU has a duty cycle < 10%, so keep the default processor. Like homes, hard disks tend to be maxed out to their capacity no matter how large the capacity is.
The following is a list of 'necessary' parts when building a computer, and some suggestions for each:
- Case (get one with good ventilation and the right form factor. Cases usually have a particular arrangement and can be reused for several cycles). Cost: $75
- Power supply (generally, a better power supply is recommended. You want something reliable, with some extra capacity (between 500W and 700W gives plenty). Ideally, it will be modular, because otherwise there will be a ton of extra wires in your machine). You can re-use. Cost: $100
- Motherboard (Go for a mid-range motherboard with the ports you think you'll need on it). Cost, with CPU: $300
- CPU (it's easiest to get a CPU/motherboard combo, so you know the two will work together).
- RAM (Number of sticks depends upon the slots on the motherboard). Cost: $75
- Hard drive Get a large hard drive, 2 TB on sale goes for roughly $100 now. For normal machines, SSD (solid state) drives are not cost-effective. When buying, although you can keep an eye on reviews, note that every type of hard drive will occasionally have failures, and people will then swear off that brand: "I had a Seagate drive fail after year, now I will only by Western Digital", and vice versa. You can reuse your old hard drives, but make sure to back up your data. Never buy a refurbished or used hard drive, however. Cost: $100
- Video card A cheap video card will do fine, unless you're expecting to do heavy-duty gaming, video editing, etc. A cheap video card is better than relying on onboard video. Cost: $80-100
Generally speaking, it makes sense to make a large up-front investment for peripherals, which can then be re-used with all subsequent computers. These peripherals include keyboards, monitors, mice, speakers, printers, etc. There is *never* a reason to buy speakers, monitor, keyboard or mouse with a computer. Just re-use your old ones. There is no replacement technology on the horizon for flat-screen monitors, and there hasn't been any real innovation in desktop input devices for quite a while. It doesn't make sense to pay twice for peripherals, particularly when they are of inferior value.
Although less durable, as noted above parts in the actual machine can be re-used for a while: case, power supply, hard drive, and sometimes RAM (if you have slots available) can be used for a few upgrade cycles.
Desktop personal computers (PCs) are made from modular commodity components. Many of these components are solid state electronics, which do not suffer from wear and tear. So, computers are often discarded with one failed component while all the remaining components may be reused. Often it is possible to get a broken computer for free, and replace a single part for less than $20 to make it fully functional again. Going one step further, it is usually possible to combine parts from 2-3 discarded computers of a similar vintage into one fully functional machine.
Components involving motors are most likely to fail:
- Hard drives (you can still extract magnets and sell it at the junkyard)
- Optical drives (CD/DVD)
- Cooling fans
Other parts that occasionally fail include:
- Operating systems (virus or user error)
- Power supplies
- Cables (copper can still be sold)
Also check Metal Scrapping to get a general overview of what you can get from old stuff.
Long lasting keyboards
Built with mechanical switches instead of the pervasive membrane switches:
Arguably the most durable keyboard is the IBM Model M, which uses buckle-switch technology. These keyboards are also known as 'clicky keyboards' because they can be noisy. You can still find 20+ year old keyboards which work fine and look brand-new. They can be pricey because they've been discontinued (you can find them for about $100), but they will last longer than you. Also, the keys are generally removable and can be cleaned independently in the sink, and then be replaced.
Actual membrane switches, but quite long-lived:
- Happy Hacking Keyboard - for PCs and Macs (switchable alt and windows key/command layout). Note that it has a slightly uncommon layout of the control, esc, backspace, and backtick keys. 
The following is a comprehensive list of 'industrial-strength' free software. That is, where the software is comparable to a paid, proprietary solution. This does not include trial runs or other seriously limited software, but can include closed-source free (as in beer) software.
Free operating systems
There are many different varieties of each. Different types of an operating system are referred to as 'distros'. Some of the most popular Linux distros are Ubuntu, Fedora, Debian, and Linux Mint. See DistroWatch for a comprehensive list of Linux Distros, alongside reviews, news, and download links.
These operating systems are inexpensive to use, not only because the software itself is free, but also because it can be configured to operate on old, cheap hardware. For instance, the lightweight Xubuntu version of Ubuntu requires only 192 MB RAM and 2 GB hard disk space. Used computers meeting these requirements can regularly be found for $50 or less.
- Irfanview Image viewing solution. Good for organizing, renaming, slideshows and image basic image manipulation
- Picasa Google's image organization and manipulation program. Good for organizing photos and adjusting tone.
- Gimp GIMP is an acronym for GNU Image Manipulation Program. It is a freely distributed program for such tasks as photo retouching, image composition and image authoring. It has many capabilities. It can be used as a simple paint program, an expert quality photo retouching program, an online batch processing system, a mass production image renderer, an image format converter, etc. GIMP is expandable and extensible. It is designed to be augmented with plug-ins and extensions to do just about anything. The advanced scripting interface allows everything from the simplest task to the most complex image manipulation procedures to be easily scripted.
- Inkscape Vector drawing, comparable to Adobe Illustrator.
- Firefox No explanation needed. The most extensible open-source browser available.
- Chrome Google's browser. Extremely fast and lightweight.
- Opera Extremely fast and lightweight. Lower memory footprint and faster than Chrome and Firefox.
- Epiphany Epiphany is the web browser for the GNOME desktop. Its goal is to be simple and easy to use.
- Midori A lightweight web browser.
- SeaMonkey Web-browser, advanced e-mail, newsgroup and feed client, IRC chat, and HTML editing made simple—all your Internet needs in one application.
- VLC Plays virtually any kind of video. Allows addition of subtitles to videos, adjusting playback speed, aspect ratio, etc.
- vim Classic *nix modal editor. One of the two 'holy editors' for text editing (the other being emacs, below).
- emacs Text editor/operating system (Fun fact: The ERE book was written exclusively using emacs.)
- Eclipse Modern IDE, originally written with Java in mind. Tons of plugins, now extensible to support Python and numerous other programming languages.
- Free world-class compilers/interpreters include gcc, clang, OpenJDK, CPython, GHC, and MIT/GNU Scheme.
- LibreOfice LibreOffice is the power-packed free, libre and open source personal productivity suite for Windows, Macintosh and GNU/Linux, that gives you six feature-rich applications for all your document production and data processing needs: Writer, Calc, Impress, Draw, Math and Base. Support and documentation is free from our large, dedicated community of users, contributors and developers.
- Evernote Take note of anything.
- LaTeX Typesetting.
- Foobar2000 Arguably the most flexible music player. Endless customization options, handles most audio formats, extensive bulk metadata adjustments, lots of add-ons. Note, however, that it only runs natively on Windows OSes.