Sodastream. Has significantly increased the amount of water i drink and conversely decreased other crap being drunk High end ricecooker ended up getting more use than expected. USB KVM style switch to change mouse/kyb over between work and personal device
I didn't technically buy a Sodastream, but it's been a great addition. We used to regularly buy pads of Lacroix from Costco. Now it's just the plain fizzy water (with occasional home-made flavor experiments).
I also use them in cocktails (about 1/4 packet per cocktail), put in first and pour cocktail ingredients over the crystals to dissolve (or shake if not using any carbonated ingredients).