This may sound silly, but:
- my hacked iPad. It's first generation, original software was stupid, but with "RedSn0w" and all of Freeman's Cydia apps, it has turned into my favourite device. It has a full, Linux-like file system, I can have all sorts of material on it, SSH works fine, can use it as a controller, and I can still browse (some) internet sites. (Using it to write this). I have Macbook Pro, a bunch of Linux boxes, couple of nice Acer laptops, but this ancient iPad is so very well made, and all the Cydia stuff just works. My partner has a modern iPhone, but I like this old iPad, where each key on the screen is half-an-inch across!
- my AR-15. AK's are prohibited where I live (and so now is my AR), but folks need to understand what a fine triumph in modular design and excellent ergonomics, the American-designed AR-15 rifle really is. Early rifle designs were just not good - soldiers would pull the trigger, and be blinded as the breech blew up in their face. The AR is light, lethal, and reliable. Like most good design, it is the result of continuous improvements over a long time span.
- The Piper PA-28 "Warrior" general aviation light aircraft. This is just an amazingly successful design effort. Everything in aircraft design is a series of trade-offs, weight, strength, durability, reliability, ease-of-use, safety, complexity, simplicity, and so on. I did all my fight training as a young fellow on Cessna 172's, which are also excellent examples of very good design. But the 172 feels like what it is, to fly - a solid, simple workhorse. The PA-28, with a 160 or 180 hp engine, manages to feel quite different - like being able to drive a Camaro around in the sky. It's not a Ferrari, but it had several fine design features that made it feel like a much more substantial and flyable aircraft, especially for a kid learning to fly. It was real fun. The wings were tapered. Compared to older "Cherokee" models, which did not have tapered wings, the difference was significant. It is, of course, a low-wing aircraft. This makes for a much more attractive flying experience - you are driving a platform, not hanging from a wing, in a little box. And this aircraft has a stabilator, instead of a tail-plane and an elevator. On the Piper, as you pull and push the control wheel, the whole rear wing tilts up and down. This is just a genius design feature, and gives the aircraft a nice lively feel, even if you are flying the cheapest, entry-level version, which does not have retractable gear. (If renting at a flying club, you probably won't have any retractables - since some student might forget to drop the gear, and may well wipe out the aircraft.) Our club had one Warrior, and it was a very big treat, when I could book it and take it away up north, for a weekend. The little design genius features, made it very fun to fly. I recall dropping the flaps involved pulling on a lever, much like a sports-car emergency brake. (On the Cessna, to put down flaps, you throw a switch on the panel, and listen for the servo-motors). But on the Piper, you pull on this lever, and feel the wind on the flaps, as you pull them down. You literally could feel the air, as you flew thru it. And with those tapered wings, and the rear stabilator, you could drop a wing and dive down quick, and the whole experience was wonderful, because of these specific design improvements over the old square ( non-tapered) wings of the older "Cherokee" models.
- lastly, (call me crazy, if you must), the original APL computer language, which I learned when very young, because it was the only interactive environment available. APL was (is) very different, but it turned out to be an amazingly useful languange and environment to learn. I met Ken Iverson (the inventor author of APL), and he and I did not see eye-to-eye on things. But APL was a work of genius. APL was very popular inside IBM in the early days, and the first IBM P/C was actually pre-dated by an IBM Personal Computer that ran APL, called the SCAMP, which came out in 1973, if I remember correctly. I still use APL applications, and we use them, because they make us money. And that is always important in any product design... :)