I've been using Spotify premium for a while for casual listening—it is especially great for sampling music you might not want to buy, but might want to rickroll party guests with.
My latest addiction, however, is Songza. Music playlists curated by actual human beings, who make decisions that computer algorithms (i.e., Pandora) just don't make. And in addition to just browsing by genre, you can explore moods, activities, decades, culture...shit like that.
Another thing I love is that when you think you've browsed down to the playlist level, there's often one more level underneath. For example, go to Concierge: Sunday Afternoon > Relaxing at Home > Laid-back Acoustic there's actually one more level down. At that level, you could pick Acoustic Guitar Instruments, The New Singer-Songwriters, or Harvest Moon.
And it's free and integrates with Sonos, so that doesn't suck.