If that wasn't cool enough, check out the catalog: http://onedropyoyos.com/yoyos/
So many of the yoyos in game are OneDrop yoyos. Greg asked me in-game the other day what the little icon on most of the yoyos' tooltips was, and I had no idea, but I do now. It's the OneDrop logo!
For example, this yoyo is the one I'm currently using. It drops at a pretty high rate in the Underworld, and I think there are a few back at the home base for anyone to grab.
Real life: http://onedropyoyos.com/yoyos/cascade
In game: http://terraria.gamepedia.com/Cascade
How cool is that? Re-Logic has a nice habit of teaming up with other gaming companies for cross-promotion, but this is my favorite so far. Terraria has made me want to buy a real yoyo, so maybe I'll get one from OneDrop when the time is right. Maybe even the Terrarian if the price is right (the Cascade is well over $100, for an example of their prices, but you can get other models for $40).