So this is my recommended way of watching Gundam. It's not the order in which I watched the series, but hey.
All series that follow the UC timeline:
- Mobile Suit Gundam
- Zeta Gundam
- Gundam ZZ
- Char's Counterattack
The next three are what I call the "side stories", since that's what they are. Even though they take place during and between other series, I feel that they should be watched after seeing the "original saga", because they were made later. You could choose to watch them in UC chronological order, through, but that would actually be kind of tricky (meaning you'd have to watch some of MSG, for example, then most of 08th MS Team, and then switch back to MSG, and then watch some Gundam 0080, and then switch, etc. You could watch Gundam 0083 between MSG and Zeta, though, because it actually takes place between them) . But you could watch them after MSG if you like. (They are all OVA series.)
- The 08th MS Team
- Gundam 0080: War in the Pocket
- Gundam 0083: Stardust Memory
The stories that take place later on the UC timeline:
- Gundam F91 (Movie)
- Victory Gundam (V Gundam)
Then we move over to the alternate universe series (AU). Each of these series, plus their sequels, take place on their own timeline. I think that it's best to watch them in the order that they were made (Other than sequels, of course. Watch them in order).
- G Gundam
- Gundam Wing
- Gundam Wing: Endless Waltz
- Gundam X
- Turn A Gundam
- Gundam SEED
- Gundam SEED Destiny
- Gundam SEED: Stargazer
- Gundam 00
There are many miscellaneous things that didn't cover here, such as SD Gundam Force (don't bother watching, in opinion), the SD Gundam series (it's a chibi parody OVA series with the cast from the original saga), G-Savior (the live action movie that I don't consider Gundam), Gundam Evolve (stand alone short episodes based off characters and mecha established in other series), and MS Igloo (which I don't know enough to tell you about).
So yeah, there's the list. Get crackin'!
EDIT 10/12/2007: There is also a new "SD Gundam" series called Gundam SEED Character Theater, which features the SEED characters as chibi.