Pigot and Co.'s Royal National and Commercial Directory
The flysheet of the 1839 edition continues ...
"... comprising classified lists of all persons in trade, and of the nobility, gentry and clergy, resident in the towns and principal villages in the above counties. An account of every mode of convenance by railway, road and water; Post-Office regulations, &c."
Alec Whitfield has compiled indexes to surnames and place names for the Kent volume of the 1823 and 1839 editions which have been republished and are fairly readily available to researchers.
1823 (available on CD from S&N Genealogy Supplies)
Pigot 1823 (Kent) surname index
Pigot 1823 (Kent) place name index
1839 (available on CD from Archive CD Books)
(facsimile edition published 1993 by Michael Winton - ISBN 0-9504069-5-3, now hard to find)
Pigot 1839 (Kent) surname index
Pigot 1839 (Kent) place name index
Other Historical Directories
Janet and Richard Mason have transcribing a number of Kent and Thanet Directories. See Janet and Richard Mason's Genealogy pages
There is a terrific selection of local and trade directories spanning the period from 1750 to 1919 on the Historical Directories website.