The excellent Cork Past and Present site, run by Cork City Libraries, has added a few more directories since the last significant upload only last month (see blogpost).
The new publications – the 1910, 1930 and 1940 editions of Guy's City and County Almanac and Directory – are available as both flip-page on-screen copies and downloadable pdfs. The latter are very large at 83mb, 67mb and 69mb respectively.
You'll find the full selection of directories, dating from 1753 to 1945 here.