Do you want something like a keepsake with sentimental value or just a really good present - something you know he'd really want.
What does he like?
Weekend away springs to mind (but then I do like gifts I can enjoy too!)
A red letter day, something he has always wanted to do but hasn't been able to yet. Like parachute jumping or sky diving, they have loads on their web site. I bought dh flying lessons from there for his 35th.
ok, I've stopped being lazy and found the personalised monopoly all by myself. (Ignore the flash download message and enter anyway)
£95 + £5 p+p
but what a great gift! It's my parent's 40th wedding anniversary next year - I'll have to remember this!
I have done the racing day at Castle Combe as dh bought it for me for my 50th. It is fantastic fun and if your dh likes cars he will love it! I was the only female and there were 19 men doing it, it was last November and it was sleeting on the day but still enjoyed it nevertheless!
I got DH a watch for his 40th - at least I will when he gets around to choosing it. My sister got him a great present - she put together a box of things from 40 years ago, mostly bought off E-bay. The items included original copies of newspapers, magazines (the NME), Beano, the single that topped the charts when he was born, a DVD of Camberwick Green (which DS loves!) - all sorts. BTW, the Monopoly board idea is ideal for my best friend, who will be 40 next year - another thanks for that.
Oh, and I got my sister a flight in a hot air balloon for her birthday. I arranged it for the actual morning of her birthday - she got up at some ridiculous hour (5am?) to get to the place, only to hang around for a couple of hours before they decided it was too cloudy to take off. Oops, sorry sis. She did it another time, though.