World of Warcraft has a very flexible Interface that can be extended using a lot of AddOns. If you want to have an optimal gaming experience, use AddOns. In this post, I will provide you with a few starting points.
First of all, there are some AddOns that are usually mandatory for endgame and leveling experience.
- SpartanUI: This is a package that “skins” your Interface to look nice. I took this one, there are probably thousands of them. Pick one you like.
- Pitbull4: This AddOn modifies your “Unit Frames” to display more information. Very handy to get all vital information about some unit you are targeting, etc.
- Grid: This is a very compact set of Raid Frames. Grid is very customizable.
- Deadly Boss Mods: This AddOn shows you special warnings on boss encounters. It basically helps you to not stand in fire.
- Omen: Omen is a so called Threat Meter, it will help you managing your threat.
- oRA3: oRA3 will help you with a lot of small things, like showing you who the Tank is, Readychecks, etc.
- HideBlizzard: Hide some stuff from the default UI to keep things tidy.
- RaidBuffStatus: Easy tool to buff groups and check the overall status of buffs on your party.
The following AddOns will make your life a lot easier, but usually they are not necessary:
- OneBag and OneBank: This changes the display of your bags and bank tab. Very useful to keep things clean.
- Pawn: This tool gives you information about gear that you find while playing. Will show upgrades in an items tool tip.
- Outfitter: This helps classes that use multiple gear sets like
Druids or Paladins. Also great if you like to role play or wear fancy stuff.
- Gatherer: This AddOn is great for gathering professions. Will remember where you found herbs, ore, and other stuff and displays it on the map. There is also a DB you can import from Wowhead.com.
- Auctioneer: Great for buying and selling items on the auction house.
- Recount: Tool for analyzing your performance in a group.
- MiniMapButtonFrame: Clean up those tiny buttons!
Finally, there are AddOns that simplify “the small things”. These are mainly time savers or statistic tools:
- CensusPlus: Tracks how many characters of which class and level are online. Great for statistical interpretations.
- Overachiever: Shows you Achievements you can do nearby.
- NPCScan: Tells you that rare Mobs are around. Good for hunters or Achievement- Addicts. 
- Postal: Upgrade your mailbox. A lot of cool features!
Of course, there are more AddOns. I consider these or similar counterparts especially useful. I’ve only posted the ones I actually use, feel free to comment on them. Some people like Carbonite, but I’m not that huge of a fan of it.
