Video Players: MX Video or Dice Player.
Comics: Perfect Viewer
Secondary book reading application: Kindle (yes, yes, I know. blasphemous on a Kobo tablet)
Audio books: Mortplayer. Allows you to bookmark spots in an audio book for later.
Also, I find ES File Explorer quite handy. When you're connected to the same wifi network as your home PC, you can access the files on your PC (as long as the PC is on, of course). I think Astro File Manager can also do this.