Sera Myu Antics has streams of them too (as well as a lot of the omake and fankan videos), although I don't know if they'll work on mobile. The subs can also be a little eh, but they're tolerable.
Otherwise yeah, YouTube is your best bet. Most of what you're going to find is subbed by either Miss Dream (who I'm not all that fond of for the older shows because they cut off the curtain calls/service numbers) or Cruel Angel (which is what's on Sera Myu Antics).
If downloading is an option, my preference is for Sea of Serenity. They've done all the musicals thus far (but not the omake/fankan content), and they're working on PGSM right now. TV-Nihon has also done all of PGSM and has been very slowly releasing new versions from the DVDs.