Well, let's get some awesome platformers out of the way:
-Ratchet and Clank series (PS2. 1-3 were good, Deadlocked was ok, Size Matters and Secret Agent Clank are meh ports of the decent PSP spin-offs)
-Sly Cooper series (PS2)
-Jak and Daxter series (PS2. 1-3 is good, X is racing if you're into that, and Lost Frontier was kinda meh)
-Spyro series (PS1. Avoid the PS2 games, especially Enter the Dragonfly)
-Crash Bandicoot series (same as Spyro)
-Klonoa 1 and 2 (1 on PS1, 2 on PS2. 1 isn't the cheapest game out there)
Now then, what else?
-Okami (PS2, in my opinion better than the Wii version)
-Ico and Shadow Of The Colossus (PS2)
-Psychonauts (PS2, but better versions are on the PC/Xbox)
-Kingdom Hearts (PS2. 1 and 2, plus maybe check out a synopsis of Chain of Memories and 358/2 Days. Skip the fat and go straight to the meatier bits of the franchise)
-Beyond Good and Evil (PS2. Not sure if the other versions are better though)
-Prince of Persia: Sands of Time (PS2, other versions available and I played it on GC. I haven't heard any significant differences in quality)