You can view which new topics have new replies today by clicking on the 'Today's Active Topics' link found at the bottom of the main board page (the first page you see when visiting the board). You can set your own date criteria, choosing to view all topics  with new replies during several date choices.

The 'View New Posts' link in the member bar at the top of each page, will allow you to view all of the topics which have new replies in since your last visit to the board.