Like most people I struggle with DH every year, not helped that his birthday is the same week!
Also he never want anything or expresses likes. He's really into reading books but mostly feeds that by using the library.
This year I am really please I managed: (this covers both BD & XM)
New toiletries bag (old one bust) filled with chocolate tablets and plasters
A waterproof high-viz cycling coat. (existing one not brill)
Spoke lights, and anything else bike-related I can think of
Keyring and mobile phone cover (existing ones worn out)
The even more boring things that crop up every year: Socks and novelty boxers...
In the past I have done (the ones I can remember):
Something chocolate: Made a hamper, or some novelty items, posh slabs, etc etc
Amazon voucher (when I was completely stumped)
Kindle (he still prefers the library)
Historical OS Map set for our area (kind of relevant to his research/work)
Watch (multiple times, even quality ones get killed eventually)
Wallet (ditto)
Belt (ditto)
Alarm clock (radio controlled is great)
A beerbods subscription
And the best thing is that my parents and in-laws also ask me if I have any ideas what to get him as they're stuck. If I had any I would not give them out 
. My parents now stick to giving some money and a minor novelty.
My DF is really quite easy - I usually find an interesting non-fiction book for him at the Book People. Travel, Explorers, Polar Regions...
My DFIL is really hard again but does like gardening so there have been plenty of options. This year tough he's getting a set of souvenir tea towels - it's a family specific present that really works.
Other adults in my families we've agreed not do exchange gifts any more. And my teenage Nephew / Godson has been getting GAME/ITunes vouchers for years now.
But I'll be reading this thread with interest!