Searching for locations, or "Geocoding", is something you can do on many map sites. This site offers location of ZIP codes for US addresses only. The database is 98% accurate and should find all zips except those registered in the last five years.
Unfortunately, a more up to date zip code search and international postal code supports costs more money than we can afford right now.
If the site proves very popular, we might add these sorts of things later. No promises though.