You can't go wrong with an awesome t-shirt, most dudes love them. Luckily, etsy is full of great t-shirt shops, here's just three of my favorites.
The boy has several Timber t-shirts and it's probably my favorite place to get t-shirts online. They have so many great designs (and them come in lady sizes too!)
I really like Dowdy Studio! This whale one is so simple and awesome. I think most guys in their 20's or 30's would like the designs from this place, they're pretty universal but still unique.
And finally, Mixed Species. I love this shop, they're so bizarre and they were the first shop I 'favorited' on etsy so I've got to give a shout out.
Alright, I'm going to try and fit one more 'Men's Gifts' suggestion in before it's too late to order online! I don't want to make any promises though, I've got to get on with my present buying too.