There are more than 12,000 regional checklists in Avibase, offered in 9 different taxonomies, including synonyms more than 175 languages. Each checklist can be viewed with photos shared by the birding community, and also printed as PDF checklists for fiel use.
You can use this page to compare any 2 historical versions of a published checklist. For example, you can use this tool to see what changes have occured between the
6th and the 7th edition of the AOU checklist, or between the 48th and the 49th supplement. New (Jan 2013): Cross-checklists comparisons are now available!
For example you can now compare any version of Clements and the IOC checklists (cross-checklists comparisons are only available for global checklists).
You can now also restrict the list of changes to a geographic region (e.g. a country, a province or a site) to see only changes affecting birds in a specific area.