The HTC Vive is one of the premier PC-based VR systems on the market, and part of the full package are two motion controllers, colloquially called "wands." Each wand has a touchpad on it that allows for locomotion and menu navigation, and while it works well, some feel that a joystick makes a bit more sense. If you include yourself in that camp, I have a solution that can help easily (and cheaply) add joysticks to your wands.
See Vive at Microsoft Store (opens in new tab)
3D-printed Vive wand joysticks
A GIF was posted in the Reddit Gaming subreddit showing a plastic joystick being clipped onto a Vive wand, and ever since, creator Eisenmeower has been getting slammed by orders on their ebay page (opens in new tab). A single joystick costs only about $7.50 (opens in new tab), and pretty much everyone who's ordered one has enjoyed it without much issue.
See at ebay (opens in new tab)
The 3D-printed joystick is simple but intelligently designed, with a clip that attaches to the wand above the touchpad and a joystick that sort of hangs down over the actual touchpad. Eisenmeower has posted the design to Thingiverse, allowing anyone with a 3D printer to print their own joystick.
See the Vive joystick at Thingiverse
What about Vive wand touch tracking?
The touchpad on Vive wands can either be clicked down or simply tapped, effectively doubling the amount of buttons without cluttering things up. Fallout 4 VR (opens in new tab) is a perfect example of a game that uses all of the touchpad. You click down to move, but you use light touches to navigate your Pip-Boy menus. So won't placing a joystick over the touchpad ruin the effect of actually touching it with your thumb?
I thought the same thing when I first saw the joystick, but because the joystick is printed using conductive PLA filament (the rest uses PLA+ filament), the wand can't tell that it's not actually your thumb touching down.
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If you have a 3D printer and have been pining for Vive joysticks, definitely give this a try. Eisenmeower's ebay page seems to still be taking orders, and at about $15 (opens in new tab) for two, these are relatively cheap accessories. For more, be sure to check out the HTC Vive accessory guide!