I know there are a lot of new people that are itching for fighting something much, much larger than yourselves. So here's a post on where all the bosses are!
Bosses also have a max level cap, like dungeons, of 10 levels. If anyone goes to a bosses, that they are too high of a level for, you run the change of bugging the boss and no drops will happen. So if you go to Argos, please make sure that you are L43. Widow Maker is L49, and so forth.
CX-1 Destroyer, Level 18 world boss, spa