I've never watched any Gundam before and watching Valvrave has convinced me I need a good mecha show (that isn't Valvrave). Any advice on where to start? Which Gundam series are good?
Good Gundam shows to start with are Mobile Suit Gundam, Gundam X*, Gundam Wing, Gundam SEED, and above all else, Mobile Fighter G Gundam.
Gundam shows to avoid like the plague they are: VICTORY GUNDAM and Gundam AGE. Other subpar Gundams include 00 (Second Season and beyond. 1st season is just fine to start with, its a bit like Full Metal Panic! and Gundam Wing, but again, not a bad place to start.) and Gundam SEED Destiny (which I am partial to, but admittedly sucks.) and Stardust Memory.
Zeta, ZZ, CCA, Unicorn and F91 are good, but you should see MSG before you see them. It's an older show, but definitely a good one. 08th MS and War in the Pocket take place at the around the same time as MSG and are good, but a familiarity with MSG makes them better (I'd say, at least. War in the Pocket is excellent either way.)
Turn A Gundam is incredible but should be saved until after you've seen some Gundam shows.
*I haven't seen X yet.