I guess since then jigsaw puzzles have not been just a hobby for me. Too often I find myself dreaming of yet another jigsaw puzzle. The only drawback is the space they need when under construction.
Buying Guide -
http://www.selonen.org/laura/puzzles. html
Antique wooden and cardboard puzzles are highly collectible - more so if they're complete. If your fanatic is interested in the history of puzzles, you may want to look in this direction.