Other than that the only non-UC thing I'd really say is a must-watch is Wing, but I'm probably ignorant of at least one or two others that are probably worth it.
Can't say I agree with this, to be honest. Wing is good but not great. Episode 30-40 is BRUTAL to get through. Treize is a top tier character, but Zechs is a pretty forgettable Char Clone.
There are definitely better AUs, most notable of which is Turn A (though opinion IS divided on it. I'll be the first to admit that while it is an amazing show, it's not a very good GUNDAM show. Watch it and you'll understand what I mean by that). 00 is pretty interesting as well since it has a very distinct post-9/11 feel to it. And honestly, I've been enjoying AGE a lot.
Really, the only AU I can't recommend is Seed and Seed Destiny. For some reason its the most popular Gundam series in Japan, but man they're pretty bad.
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"One of these days, I'm gonna find a loophole my friend." - Man in Black