So, I'll start with my list of recommendations and I hope other people will follow along with their favorites below...
You can download software for add-ons at Curse Client: http://www.curse.com/client.
- AtlasLoot - http://www.curse.com/addons/wow/atlasloot-enhanced - For helping me find good-looking transmog (or, easy adult entertainer) gear! I can browse through old content loot within WoW and see what things would look like on my character.
- Recount - http://www.curse.com/addons/wow/recount - Basically it's to check my healing numbers, and compare such numbers to other healers, during a fight or an overall instance (like, throughout the entire raid). It has a section separated off for DPS counts too but I never DPS.
- Deadly Boss Mods / DBM - http://www.curse.com/addons/wow/deadly-boss-mods - Sometimes it's just helpful to know what's up-and-coming in the fight. It gives me some visual and audio warnings.
- MyRolePlay / MRP - http://www.curse.com/addons/wow/my-role-play - So, I don't actually use MRP but I've been recommended it a ton of times. Apparently you can put a description of your character and/or your RP preferences for others to check out!