There's a neat connection you can create using Hook and DEVONthink. Hook is a program that creates a palette of connected items throughout your system. I've described using Hook before when using it with OmniFocus.
Using Hook, you can automatically create a text file in DEVONthink to connect to any other part of your system.
As an example, here's a project I have in OmniFocus:
I then
Doing so summons the Hook app, which you can see hovering over the project in the OmniFocus window:
In the image below, you can see the menu option that could alternatively by selected:
A new window appears asking where you want the note in DEVONthink:
Once you do, you'll see a new note, ready for whatever reference items you want to add:
Now, whenever you select the OmniFocus Project and invoke the Hook command, you can see your reference note:
Setting it up is easy.