There are 31 collections now available, representing hundreds of historic newspapers for your research.
On September 12, 2015 he published an update to the list. The lists include free, subscription and library-based collections.
This is a list of links, not a site where you can search the actual online repositories.
The lists are very well organized by locations, including city and county. Start and end dates for the newspaper publication dates are also included.
If you are researching British and Irish newspapers, this is as "must visit" site.
The link is Richard Heaton's Index to Digitalised British and Irish Newspapers Online (updated 12th September 2015)