It's difficult to tell what is the best gift for guy because there are many things you can send, for example, wallet, pen, phone case, brooch, leather bracelet etc. You need to know what he likes first, and then you can choose a gift that suit for him. Once I bought bracelet on pandahall for my brother, and my friend told me that a wallet is better, but my brother loves the leather bracelet very much. So it's hard to say that what is the best.
I just found this great new site, goombarterboom.com They have great stuff at cheap prices that other people are selling. Doesn't mean it's used. Lots are brand new. If he's into sports, you could buy him men's shirts and hoodies with his favorite team logo. If he's into jewelry, there are some really nice stainless steel men's bracelets. Nice watches too. If you browse around you may get other ideas too. It's goombarterboom.com
With guys, sometimes an experience is better than a tangible gift. Maybe taking him to a movie he's been waiting to see, or you could give him the opportunity to go with him wherever he wants for an entire day. Don't forget, coupons for chores also make great gifts, and I know a couple of guys who would enjoy a new book, or a gift card to a favorite restaurant or shop. I know a couple of people who go straight up and ask the guy what they want as a gift. Asking can help you find out his exact wants.