Is it possible to find the serial number of stolen devices using a Mac that they've been connected to?
How to get serial numbers for displays:

Go to /Library/Preferences/com.apple.windowserver.plist. Open this with TextWrangler or a similar utility. Look for a DisplaySerialNumber key with an integer value that isn't 0. With any luck, this should be the s/n of your display.
If you haven't used this display for a while, the records of it may be gone.
Also, it appears that this isn't guaranteed. Double-check if possible.



How to get the serial numbers for iPods:

Open /Library/Preferences/com.apple.ipod.plist.
 Look under the Devices dictionary. Any iPod you've connected will have all its info there, including the s/n (under Serial Number).

Good luck.