RPG wise, the PS1 & the PS2 are the best systems ever.
Can I get an "Amen"?
I haven't been through all of the posts but, if Castlevania: SotN, Alundra, and Klonoa aren't listed...they should be 
There's a lot of great PS1 games but - unfortunately, now's not the best time (unless you get lucky) for finding a lot of them on the cheap 
Nothing touches the PS2 when it comes to JRPGs, but the PS1 is a strong second place. And all three games you named are amazing - SotN is in my top-3 all time, and Klonoa is just an amazing game. Both of those are a little pricey these days, but fortunately there are tons of ways to play SotN and Klonoa got a really good Wii port that I highly recommend (just for the love of all that is holy, go into the options and switch the vocals back to the "gibberish talk" they were originally).
I haven't seen anyone mention these gems:
Ape Escape
Wipeout 1 & 2
Crash Team Racing (still one of the all-time best kart racers)
Survival Horrors? Any of the Resident Evils, Dino Crisis...
JRPGS? Anything with Atlus on it. Though if you're looking for good rpgs that aren't the typical square fluff you're probably going to be spending a pretty penny (over thirty dollars).
Spyro was pretty great, btw!
Square was in their prime during the PS1 & most of the PS2 days. It's an injustice to dismiss their PS1 output as "fluff" IMO - even beyond the main FF7-9 games you had games such as Xenogears, FF Tactics, Parasite Eve, Brave Fencer Musashi, Vagrant Story, Front Mission 3, Threads of Fate and Chrono Cross. Probably more I'm leaving out. Sure, if you ONLY played Square RPGs from that system you're leaving out a ton of amazing games, but ignoring them is just as much of a crime.
