Convert lat/lon to zipcode / neighborhood name

You can now do this directly within R itself thanks to the rather awesome ggmap package.

Like others mention, you'll be reverse geocoding using the google maps API (and therefore limited to 2,500 queries daily), but it's as simple as:

library("ggmap")

# generate a single example address
lonlat_sample <- as.numeric(geocode("the hollyood bowl"))
lonlat_sample  # note the order is longitude, latitiude

res <- revgeocode(lonlat_sample, output="more")
# can then access zip and neighborhood where populated
res$postal_code
res$neighborhood