For Gundam, I really do recommend all of the Universal Century (MSG, Zeta, Double Zeta, 0080, 0083, F91, Char's Counter Attack, Victory, 08th MS Team, IGLOO, etc.) fantastic story with an amazing universe. IMO, definitely worth everyone's time.
Though for AU (alternate universe) Gundam titles, I think my most recommended is Turn A Gundam. The designs were done by Syd Mead (Bladerunner, Alien, etc.) with the direction of Yoshiyuki Tomino (original Gundam creator and responsible for most of UC). It's kind of like Gundam meets Ghibli, and most of my friends that I had watch it, really enjoyed it.
Bubblegum Crisis is a battle suits anime, not mecha. There's a difference. And it will always be one of the best ever made. Killer soundtrack, too.
So then these don't count for mecha?
Though the hardsuits are definitely battle suits. And agreed, that soundtrack is killer.
Some of the people I know suggest Code Geass, but I haven't watched it.
Well, if you like CLAMP, Gundam or Death Note, then I think you'd probably enjoy Code Geass. S1 is definitely better than S2 (just like 00!) but it's worth an entire watch through.
Though you really don't like Gundam X? Even after watching the original MSG? I thought it was a lot stronger than Wing, even in the shorter time span it was allotted. But then again, I also think Destiny is the weakest in the entire Gundam metaverse.
I hate that one (though I think the Destiny Gundam's design is sweet). So I suppose to each their own.