What are some good add-ons for World of Warcraft?

Answer 1

The kind of addons you'd like vary a bit depending on your role. I will try to break it up by category.

All roles

Good addons for raiding are Grid or Vuhdo for organising the people in your raid in a manner you like. It is actually almost always useful. Second, a good threat meter like Omen or the one included in Skada can help you not pull aggro (if not a tank) or see who's creeping up on you (if you are a tank).

If you need more buttons than the Blizzard action bar provides, you can use an addon like Bartender to change the look and size of your bars.

For raiders, a Bossmod like Deadly Bossmods or DXE (Deus Ex Encounters) helps in predicting and warning for boss abilities. PvP players can use Proximo to get information they need on their opponents.

Damage-dealer

There are quite some class-specific addons that can help in many features of your class, like ForteXorcist for warlocks or Serenity for priests. Skada or Recount are good damage meters, which not only tell you how much damage you dealt, but also how it was divided and what spells you used. This can help you improve your game.

Tank

Tanks need a lot of information, and usually they get it through Scrolling Combat Text (SCT) or Power Auras, both of which can be customized to show the info you need at the right time, such as boss abilities, enemies using a defensive move or a special defensive ability coming off cooldown.

Healer

If you are a healer, consider using Vuhdo as your raid frames, since it is easy to set up and can show your heals, how much you are healing, how long they will last and so on. Addons like Healbot can help in managing debuffs on your friends.

Not quite an addon, but the inbuilt macro system (/macro) allows you to create macros that cast spells by hovering your mouse cursor over a unit frame or mob instead of targeting it. Especially for healers, this can save you a lot of time.

Answer 2

First off, what class are you playing? If you are playing a class that has the talents to heal, then you should get Healbot, etc.

If you are looking for raiding or general addons, there are thousands to choose from.

Curse gaming is a good site, where many people get addons, there you can pick what you want or need.

See links.