Family tree charts
Most of the genealogists I know go through a lot of family tree charts, pedigree charts and family group sheets and prefer to gather most of those for free online or at their local libraries. However, there are specialty items, poster sized charts, and other goodies that may be perfect for a genealogist.
Scrap-booking materials
Archival quality preservation materials
Eccentric genealogist clothing
Family themed home and office gifts
Books! Because I am a librarian by trade, I always love receiving books as gifts. And looking through thrift stores for books. And looking through commercial bookstore for books. Consider buying a book about genealogy or a certain local history book for your friendly genealogist!