I know what Gundam is, but I've never delved deep into the franchise so I'm not quite sure where to start or what to watch. The ones I've been recommended, and seen, are:
08 MS Team
War in the Pocket
Thunderbolt
And I already know to avoid Gundam Wing and that one where it's set in the future and Gundams are used in a fighting tournament or something.
08 and War in the Pocket are great.
I liked Gundam 00 when I watched it years ago, but I can't remember much. Liked it about as much as I hated it's movie.
The magnum opus is definitely Gundam vs Hello Kitty