Adding a button to the lower left of each forum page marked "Previous thread" and one to the lower right marked "next thread" would allow easy traversal of the forum.

Ideally, if you are in search results, the next and previous would refer to the search results. In addition to the results of a specific search, next and previous should also apply to "Today's Posts", "Latest Posts", and "Posts since last login" (which are usually search results under the hood of the website).