natur enemy castbar (NECB) - http://www.curse.com/downloads/details/2786/
shows casting bars of enemies (which is provided in game) but has many other useful functions such as PvE cast bars for numerous PvE abilities, and most importantly, duration timers that can track stuff from spell duration to diminishing returns (vital for proper usage of cyclone and root in pvp).
outfitter - http://www.curse.com/downloads/details/7446/
basically this program (along with another similar one called itemrack) allows you to make pre-set collections of gear (gear sets), name them whatever name you want, and bind them to a key on your keyboard (also you can select them manually from a small pull down menu). great for a druid since we often carry a LOT of gear and hitting a single button to switch from DPS to healing gear is much nicer than switching in 16-18 unique items by hand.
x-perl unit frames - http://www.curse.com/downloads/details/3416/
customizable unit frames that allows you to move, resize, and texture the target, party, character and various other frames the game provides. also provides a "focus" frame which shows the portrait (and thus allows you to manually click or keep tabs on vital information) of your current focus target, if any. the REAL good thing about x-perl is that is has the healer deficit feature (present in other mods, but i like x-perl pesonally). this feature switching the health bar readout and reversed the display of information. so instead of seeing a person with 10,000 life at 100%, you see a person with 0 damage at 100%. as the person takes damage, the meter that represents their life bar begins to fill with the corresponding damage they are taking shown in place of their HP. in other words, the deficit feature tracks how much health a target has lost and present that lost health instead of showing you how much remaining life they have. VERY nice as a healer because its easier to see "i need to heal 1500 life" instead of seeing "ok, he has 10k health and is at 85% so i need to heal....carry the one....root 2....1500 life!"
x-perl also has a nice out of range heal feature where you can set all targets out of range of a specific spell (defaulted to healing touch for a druid) to "gray out". thus, at a glance, you can tell if someone within range needs healing because youll have your deficit listed and their portrait will be highlighted, indicating they require healing and are in range. great for BG's when you get put in a random group, as it helps stop the "i need to heal my party members but theyre apparently out of range!" problem that often crops up.