OK, here's a start, anyway.
For apps, there are lots. You already have Pandora, you said. There are any number of subscription music sites that will let you listen to music you specify. I like Mog because 1) it has, currently, the best SQ, and 2) it will let you download music to your device and take it with you (make sure you choose "high quality streaming" and "high quality downloads" in "options"). But there's also Spotify, Rdio, etc. Look at Wolfgang's Vault and the various Archive.org apps for live concerts: they're both fantastic. I like the NPR music app a lot - it collects the various NPR music broadcasts in one place. There are podcast apps that will collect music podcasts for you. There are a lot of radio apps that make it easy to stream internet radio - look at TuneIn, Stitcher, Slacker, etc.
For home or desk use, the iStreamer DAC has a great reputation. With the iPad you can add the Apple Camera Connection Kit, which has USB out, and use a huge range of USB DACs. They don't all work: search here, there's a lot of information on which do and don't.
For portable use, you can add an LOD and amp - both the Touch and iPad have very good SQ out of the line out - or go further and and use the Algorythm SOLO or Fostex HP-P1. Both take direct digital out. With the SOLO you'll need to add an amp, with the Fostex you won't. Both sound great. With the iPad you can use the camera connection kit and a number of portable DAC/amps - again, search here for guidance.
With the portable set-ups you'll be able to stream both wi-fi and cellular from the iPad, wi-fi only from the Touch.
Hope this helps.
