Citi's Costco Membership Card
If you're already a Costco member, this is a "set it and forget it" keeper for gas, dining, and travel. Just know your cash back doesn't show up monthly—it arrives once a year as a certificate you redeem at a U.S. Costco register (you can take cash if you don't spend it all).
No foreign transaction fees is a nice touch for international trips. Bottom line: great value if Costco (and Costco gas) are in your routine; less exciting if you want flexible points you can transfer.