http://www.world-airport-codes.com/ has almost all global codes, excluding some private fields and military airports.

The IATA website has a comprehensive airline code list but not airports. The question of "top 500 or so" depends on the measure. There are such lists on a number of metrics but usually are in different places. Ones I know of are:
1) physical size,
2) number of runways,
3) length of runways,
4) number of flight operations,
5) number of airline flights,
6) number of passengers handled,
7) number of destinations served,
8) number of scheduled flights,
9) number of international flights,
10) number of connecting passengers.

Depending on what of these metrics you choose you may find the #1 airport to be:
Beijing, Atlanta, Heathrow, Van Nuys and so on.

So, once you know the question you're asking there will be a list somewhere, using some search engine or another.