Oh my, this shall be fun indeed.
In countdown form:
10. The O: It's slow and clunky looking, but damn if Scirocco didn't own some peeps with it.
9. ZZ Gundam: It might be big, it might be slow, and it might be still out there post-First Neo Zeon War and never see battle again, but it's a pretty cool design. And it took out Haman Karn of all people. Too bad Judau didn't show up with it in Char's Counterattack.
8. Master Gundam: The Gundam of the Undefeated of the East himself, it's such a shame there are people out there who think the design stole from Epyon...
7. Gelgoog (Char Custom): What a shame the Gelgoog got such a short stick. Technically superior to the RX-78-2, Amuro's growing Newtype powers simply overwhelmed Char and the Gelgoog never saw more than two brief sorties. Nonetheless, the Gelgoog remains an awesome piece of Zeon weaponry.
6. Hyakku Shiki: Ah yes, Quatro Bajeena's custom mobile suit painted gold just to stick it to the Titans for over-looking the production of the model. Gundam ZZ's Beecha would go on to pilot the suit, but unfortunently it met its end while under the care of a boob.
5. Zeta Gundam: Oh dear, the awesome Zeta Gundam...in the middle of the list? I am afraid so, friends. Kamille and the Zeta will forever be synonymous with each other, espicially in the epic final confrontation with Scirocco in which Kamille triggered the bio-sensor and gave us one of anime's most splended kills.
4. Blade Liger (Van): Oh my, a non-Gundam mecha at last (bare in mind I am creating this list from #1 down)? Indeed such is so, as the Blade Liger is quite awesome. Zoids: Chaotic Century was a great Shônen journey, and seeing the Shield Liger evolve as Van and Zeke did throughout the show was loads of fun.
3. God Gundam: The Gundam that won Domon the title King of Hearts from his Master. The God Gundam supported Domon during the most trying battles of his participation in the 13th Gundam Fight and with it's Hyper Mode is quite awesome looking.
2. Gundam 00 (Raiser): Such a well-designed beast that was a symbol of Setsuna and Saji's partnership throughout Season Two. With it's ability to quantize it is by far the most facinating Gundam I have ever known.
1. RX-78-2 Gundam: The original Gundam, the sexy beast it is, is simple and mighty.