In the USA, SAN seems relatively close. Beyond that, I'd say DCA, MSP, MDW, LAX (you can at least walk to hotels, restaurants and stores--I've done it), maybe Tampa.

In Europe, NCE is good. I think it's officially only a couple miles from the center of Nice. It's also in a nice location along the sea.

For Asia, the old Hong Kong airport was very close to parts of Kowloon. The old Taipei airport was also pretty close. Otherwise, SIN, HND, the domestic Osaka airport, and Gimpo.

AEP (domestic airport) for Buenos Aires. Similarly, São Paulo has a domestic airport.

Cairns.

For me, the more important question is whether the airport has quick, frequent, and cheap public transportation to where I'm going in the city (without subway transfers, taxis, etc.) that works with luggage and ideally isn't subject to traffic delays.