I like MX Player for video and Doggcatcher for podcasts. For audio I use Google Music and rdio.
For music, I use the stock HTC music app. For video, mostly VLC but occasionally the stock HTC video app.
Listen to audio books and want to save/use bookmarks frequently? Use Astro Player Pro.
I mainly used Rdio and Subsonic (dSub fork) but when I'd use a secondary device as just a media player I found Shuttle+ to be the most basic, and simple player. PowerAmp always felt too bloated to me.
There are a lot of apps for music out there. I use Google Music because I subscribe to the All Access service. I've used, Spotify, Poweramp, Winamp, 8Tracks, Mspot (before Google Music existed), UberMusic, Songbird and We Are Hunted. For podcasts I've used the Listen app but, I love Pocketcasts. I'm not a big audiobook listener. My girlfriend is and she'll buy me Audible books every once in awhile so that's what I use. I don't really watch a lot of local video; mostly streaming (youtube, vimeo, netflix) but I've used MoboPlayer and MX Player before.