The announcer packs for Dota 2 are easily some of the best purchases available within the free-to-play game. Personally, I go back and forth between the Stanley Parable and Bastion announcers. Not only are they high quality, but the games themselves are amazing!
Another soon-to-be fan favorite announcer is now available for purchase: the Rick and Morty announcer pack. PyrionFlax, a popular Dota 2 figure, helped write the lines while Justin Roiland provides the voice for both characters. I've only just begun watching the televisions series, and it hasn't quite won me over yet. Maybe one day if it does, this will be my go-to announcer pack.
The pack is $7.99 and includes both announcer and mega-kill lines. You can buy it here or in-game.