What are the best gifts to buy for men?
Similar to women, you find out what he enjoys and cater to that. Really, any gift, no matter the gender, is about thoughtfulness and showing how well you know the person.
Does he like electronics? Buy him a nifty little gadget in his favorite brand. Men tend to be very opinionated on electronics brands, so if he's a Samsung freak, don't buy him Sony.
Does he like hunting? Maybe a subscription to his favorite magazine, or a box of shotgun shells.
Does he like to go four-wheeling? Jeep or Samuri, he'd probably love a bumper sticker that says something like, "H2 Recovery Vehicle."
These same tips apply for anything he likes, be it motorcycles, cars, sports, photography, and so forth. Find something that relates to his favorite hobby and give it to him.
If he really wants something for his office, I personally would recommend you gift it in the same manner you would want an office knick-knack or household appliance gifted to you -- paired with something cooler and related to the personal interests of the recipient.