Phaster: Search Discussion Boards - Search a selection of discussion groups including All Experts, Blog Hop and Google Groups. - http://www.phaster.com/find_info_deja.html
BoardTracker - Searches a wide variety of forums organized by category, includes email or IM alert capability. Basic functions are free, advanced ones require paid plan. - http://www.boardtracker.com/
BoardReader - Searches a variety of message boards and forums in 14 different categories. - http://www.boardreader.com/