Unfortunately, I don't have access to a lot of the side materials. The ones I have read tend to be more UC (though I do want to snag some Wing stuff) which is the universe I tend to prefer. That being said some of the UC side stories sound so ridiculous I'd rather just ignore them. I did read bits and pieces of "The Plot to Assasinate Ghiren Zabi" and I enjoyed that. Would Mobile Suit Gundam: The Origin count? It's got an animated piece now, but as far as I know it'll only cover the flash back volumes of the manga (which is fantastic btw, available in hardback even). I basically consider that manga to be something of an alternate universal century.

I definitely want to get at some point:
Blue Destiny
Anything Wing related
the new 0083 manga (the artwork is so pretty)

tl;dr I'm definitely interested in side stories