Other people answered already but
Dungeons have cosmetic skins, also tonics, runes and sigils, armor and weapon sets. Some dungeons actually have some functionally useful unique equipment like Monk runes from Ascalonian Catacombs or Aristocracy runes from Caudecus's Manor (used for healing builds and specific warrior builds respectively.)
Fractals are the main supported 5 man content. I would say they are a decent sized focus of the game. There are currently 18 mini dungeons. Doing fractals will give you currency which you can use to help get Ascended gear, a few unique skins, infusions, etc. Not as much a focus on cosmetics as pure dungeons.
As for Raids, each specific raid boss (there are 13 at the moment) upon defeat will have a chance at dropping a specific unique piece of equipment or mini. Doing raids will also get you currency that you can trade for the skins directly or trade for generic ascended gear if you want to gear more characters or something like that. There are also some raid specific infusions or tools like a bundle item that allows you to make portals for people.
The one thing that put me off was the amount of tokens you got for doing dungeons - I didn't want to run the same dungeon X many times just to get one piece of gear. I always felt there should have been a single "dungeon" currency that you could accumulate doing all of them...
What's the token requirement like in raids? How many times would you need to run it to get a bit of gear?