Reddit mentions of Duralex 12 Piece Bowl Set of Six, Clear

I'll throw my vote in for a sharpening stone. If he doesn't already have a nice sharpening set, maybe consider getting him something like a nice diamond sharpening stone; I've seen them for $50 or less.

Tools are always nice. Here are some suggestions to think about:
~ microplane grater
~ Japanese mandolines can be fun to have around.
~ Fish spatulas can be a handy tool.
~ Does he have a good quality peeler? Everyone has a "normal" peeler, but I like to have a good quality horizontal peeler, like one of these, to use sometimes.
~ Does he do a lot of baking? If so, maybe some silicone baking mats for his baking sheets, or maybe some parchment paper.
~ Does he like to use fresh citrus juice very much? Does he have a citrus reamer?
~ Does he like to use fresh garlic? Maybe a garlic press?
~ Silicone spatulas?
~ Does he have a pepper grinder for fresh ground pepper?
~ Does he have a set of mise en place bowls or something to use to keep his stuff organized when he's working?
~ Does he have a scale? You can find plenty of options for home-use digital scales that can weigh up to 11 or 12 pounds, and use either pounds, or grams (if he's doing anything metric.)
~ Something like a good quality cast iron pan can be a lifetime investment, because if they're well cared for, he'll be able to pass it on to his grandkids someday.
~ A dutch oven will always be useful to serious home cooks. The enameled cast iron type are very popular, but they come in many different sizes and shapes, so keep that in mind when picking one out.
~ Knives are always nice. Paring knife, utility knife, serrated slicer, etc.

Those are just a few suggestions that popped into mind. Good luck, I hope you find something nice for him.