Are you interested in finding highly cited articles? If so then the new features in UKPMC will be of value to you. Search results can now be sorted by the number of times articles have been cited.
Each search result is now shown with a count of the number of articles citing that record. If you click on the count, this will display the citing articles, which themselves can be sorted by citation count. The same functionality is also available under the "Citations" tab when viewing an abstract. As always your feedback on the new features is welcome.