Kitbashed, textured and rendered in TrueSpace 3.2
Millennium Falcon version 2 by Iven Connery
Millennium Falcon version 3 by Andrew Crook
Ah! DA ate my comment!
I was originally trying to emulate the forward spikes off the first set plans and model plans they'd drawn up for the revised Falcon, but then ultimately never added to the ship. You can see them in RM's paintings.
Story-wise, they're sensor jamming technology developed late in the war to block droid scanners specifically. It won't keep you out of sight of a battleship's scanners, but the smaller droid fighters won't be able to target you directly. These were only installed on friendly freighter captain's who helped the Republic directly with supply runs or covert missions.
Later on, the ship's engineer will find new creative ways to implement them so they keep them attached to the ship.