DPs: Lenovo earned 3X when paying through PayPal as it codes as Merchandise - ELECTRONIC STORES. Also made a small purchase directly through them and it coded differently as Merchandise - DIRECT MARKETING/DIRECT MARKETERS and did not earn 3X as a previous DP noted. That MCC is also what Nike.com and eBags.com uses and does not earn 3X, so I don't know if it's worth mentioning in the wiki that DIRECT MARKETING/DIRECT MARKETERS generally doesn't earn 3X.
Google Project Fi monthy recurring service didn't earn 3X as Services - CABLE,SATELLITE,PAY TV/RADIO SERVICES but that should earn a category bonus on a card with a telecommunications bonus category such as the Ink or FlexPerks cards.
Discount retail gift card site CardCookie did earn 3X. Should be viable for a long time as it codes as Merchandise - HOBBY,TOY / GAME SHOPS.