Repost: Quick reply failed to work, so posting a more "advanced" reply
I find this site to be incredible useful for tracking world bosses:
http://us.gw2stuff.com/events/sanctum-of-rall
This list includes checkmarks you can use to note which events you have already completed (for the bonus chest), allowing additional filtering on the list. It also reveals some of the leadup events (especially for the temples, like which beacon the Dwayna escort mission is on). Additionally, there are timers to indicate when a boss "window" will arrive, and how long an event has been running (so you can arrive late to the party if you know the boss takes an especially long time to defeat).
As far as "finding champions" easily, I've found that certain areas are prone to champion farming - Queensdale in particular has a boar, spider, troll, and oakheart that spawn regularly and are farmed by lots of people.
I've also found that on one of my early norn storyline quests, I have to go into the Jotun encampment in Wayfarer Foothills and defeat a champion-class boss. The quest takes less than 2 minutes to complete, and after defeating the boss (and receiving my loot drop), I can waypoint out of the quest and repeat. Due to the speed and simplicity of the quest, and the close proximity to the waypoint, I can farm this boss indefinitely (or at least until I complete the last step of that quest). I transfer the champion loot bags to a level 80 character for a chance at better rares/exotics, and then use the Mystic Forge to transmute rares to exotics, as needed. Easy, peasy, lemon squeezy.