Main games: All of them (except Japanese Green; I've only played games released in the US). So RBY, GSC, RSE, FRLG, DPP, HGSS, BW1/2, XY, and ORAS. And I intend to play both Sun and Moon once those come out. (I don't have an FR cartridge, though.)
Spinoffs (probably forgetting some):
Stadium 1 and 2
Colosseum
XD
PBR
Pokemon Puzzle League
Pokemon Snap
Pokemon Puzzle Challenge (on VC, never bought the original)
TCG (only 1, would like to play 2 with a translation patch at some point)
Pinball
Pinball R/S
Pokemon Channel
All of the Rumble games
Shuffle
Picross (only once though, didn't like the way the system was laid out cost-wise)
Dream Radar
PMD Blue Rescue Team, Explorers of Time/Darkness (not Sky, sadly), Gates to Infinity, PSMD
The spinoffs I can think of that I have NOT played include:
Ranger series (didn't like the don't-have-Pokemon-permanently component, and never ended up trying it)
Conquest
Hey You, Pikachu
Dash
Trozei
Pokken Tournament
Pokepark games