These addons/programs are very useful to a Feral Druid:
Rawr Gear Ranker - Rawr is a program for comparing and exploring gear for Bears, Cats, Moonkin, Healadins, Retadins, Mages, ProtWarriors, Trees, Hunters, Tankadins, HealingPriests, ShadowPriests, EnhShams, and DPS Death Knights, in the MMORPG, World of Warcraft. Rawr has been designed from the start to be fun to use, and helpful in finding better combinations of gear, and what gear to obtain. You can upload your armor from the WOW armory in seconds and it will show you potential upgrades for each slot.
BadKitty - BadKitty is a debuff timer for Kitty DPS. A debuff timer is pretty essential to manage your energy, cps and debuffs to maximize your DPS.
ItemRack - ItemRack is a gear manager so that you can swap different gear sets with just a click or two.
Omen Threat Meter - It is very easy to pull aggro with Kitty Swipe so it helps to know where you stand on a mob's hate list. If you are consistently leading threat amongst DPSers, ask a war to put vigilance on you.
QuickMark - Quicker Marking of Mobs for tanking.