Is there an app that will let me drag/drop and copy/paste across two Macs?
The app can do that can do what you want is Apple Remote Desktop. You can drag&amp;Drop files from desktop to desktop and get and push clipboards from and to other computer.

The best set is to have 2 monitors (having the remote desktop fullscreen-ed), so that you can stare at the two computers at the same time. If you don't, you will have a window with the desktop of your second mac.

Another advantage of this solution is to you only have one keyboard and one mouse in front of you. And you can also put the second computer away from your desk. You just need to have it connected to you network.