Not that I'm really running after more gadgets, but sometimes, there is a need that could only be soothed through new hardware.
Bluetooth UE roll
Got this for my wife, to play music when staying out on the quays of the Rhône, playing music in the kitchen (from a phone or computer), or when she's at the photo lab.
It works well with iOS, MacOS X and Linux. It's very easy to use, with whether it's paired, connected completely obvious, and the charging doesn't need specific cables (USB!).
I'll need to borrow it to add battery reporting for those devices though. You can find a full review on Ars Technica.
Not a gadget per se, but I bought some, used it to fix up a bunch of cables, repair some knickknacks, and do some DIY. Highly recommended, especially given the current price of their starter packs.
15-pin to USB Joystick adapter
It's apparently from Ckeyin, but you'll find the exact same box from other vendors. Made my old Gravis joystick work, in the hope that I can make it work with DOSBox and my 20-year old copy of X-Wing vs. Tie Fighter.
Microsoft Surface ARC Mouse
That one was given to me, for testing, works well with Linux. Again, we'll need to do some work to report the battery. I only ever use it when travelling, as the batteries last for absolute ages.
Logitech K750 keyboard
Bought this nearly two years ago, and this is one of my best buys. My desk is close to a window, so it's wireless but I never need to change the batteries or think about charging it. GNOME also supports showing the battery status in the Power panel.
Logitech T650 touchpad
Got this one in sale (17€), to replace my Logitech trackball (one of its buttons broke...). It works great, and can even get you shell gestures when run in Wayland. I'm certainly happy to have one less cable running across my desk, and reuses the same dongle as the keyboard above.
If you use more than one devices, you might be interested in this bug to make it easier to support multiple Logitech "Unifying" devices.
Got this from a design shop in Berlin. It should probably have been cheaper than what I paid for it, but it's certainly pretty useful. Charges up my phone by about 20%, it's small, and charges up at the same time as my keyboard (above).
Bought about 2 years ago, to replace the monitor I had in an all-in-one (Lenovo all-in-ones, never buy that junk).
Nowadays, the resolution would probably be considered a bit on the low side, and the touchscreen mesh would show for hardcore photography work. It's good enough for videos though and the speaker reaches my sitting position.
It's only been possible to use the USB cable for graphics for a couple of months, and it's probably not what you want to lower CPU usage on your machine, but it works for Fedora with this RPM I made. Talk to me if you can help get it into RPMFusion.
Shame about the huge power brick, but a little bonus for the builtin Ethernet adapter.
This is probably the biggest ticket item. Again, I didn't pay full price for it, thanks to coupons, rewards, and all. The work to getting Linux and GNOME to play well with it is still ongoing, and rather slow.
I won't comment too much on Windows either, but rather as what it should be like once Linux runs on it.
I really enjoy the industrial design, maybe even the slanted edges, but one as to wonder why they made the USB power adapter not sit flush with the edge when plugged in.
I've used it a couple of times (under Windows, sigh) to read Pocket as I do on my iPad 1 (yes, the first one), or stream videos to the TV using Flash, without the tablet getting hot, or too slow either. I also like the fact that there's a real USB(-A) port that's separate from the charging port. The micro SD card port is nicely placed under the kickstand, hard enough to reach to avoid it escaping the tablet when lugged around.
The keyboard, given the thickness of it, and the constraints of using it as a cover, is good enough for light use, when travelling for example, and the layout isn't as awful as on, say, a Thinkpad Carbon X1 2nd generation. The touchpad is a bit on the small side though it would have been hard to make it any bigger given the cover's dimensions.
I would however recommend getting a Surface Pro if you want things to work right now (or at least soon). The one-before-last version, the Surface Pro 3, is probably a good target.