There's also a treasure goblin now that sometimes gives you 100 gold at the start of the game.
Was that part of the Eternal Conflict update?
~SE++
Yeah. For an unspecified duration, Treasure goblins spawn if anyone in your party hasn't yet killed a treasure goblin. Kill it before the countdown to game start finishes, and your first time killing it each day grants 100 gold.
For Gold in general, Between that and daily quests awarding 2-8 hundred gold for a similar number of games (except "win 3 games" awarding 600 for what's usually 3-4 games if you play vs. AI), it's not too hard to make a bankroll. Getting Free to Play heroes to level 5 for 500 gold a piece has also been instrumental in my current status being solvent with several heroes. (I did the math, and quests, leveling every hero that's been FTP to 5, and reaching player level 40 are near even contributions right now, having earned a total of 53k gold. Since the other sources are one-time, quests will begin to outstrip the others)
~Fake Edit~
Top Trending Heroes, huh? Man, I'd probably have to google stats. Since I don't have 10 yet to play hero league, I mostly see a lot of whoever's free this week, some of whatever's new and shiny (Johanna and now Butcher), Frequent Valla (A lot of people have her for free and she's 2k otherwise) a smattering of gold-cheap characters (Rayor, Li Li, and Malfurion mostly, maybe a bit of Gazlowe), and the occassional Nova, Abuthur, and/or Illidan. I've probably seen everybody, but anyone not falling into one of those categories is pretty scarce. Again, that's not a competitive meta analysis, just my perception as a casual player.