basically, I would make your search results page a form with checkboxes. Then the page that processes that form would add the selected IDs to another table that ties the current user ID to the selected user IDs. Then for the favorites page, you select all the items from the new table that match the current user.
You could also do this with sessions, but the database method has the advantage of persistence - i.e. the user can return to their favorites again and again.
YOu could also make the favorites page editable so they could remove favorites with a check or something.
not really all THAT difficult... :-)