Vib Ribbon, Parappa, and UmJammer Lammy!

I've been doing this myself, collecting PS1 games that as a kid with no money, I couldn't afford. The holy grail is Legend of Dragoon but that is available on US PSN, so you might be okay.

Fighting games were king back then so look for Rival Schools, Star Gladiator, BloodyRoar (2 is all I have), SoulCalibur, The Street Fighters (EX2 and Alpha 3 are best), X-men vs, Marvel vs, X-men Children of Atom, X-men Academy 2.

Fighting games seems to age better, same with platformers. You already have some of those listed, but try Croc or Gex as well.

The other games that age well are puzzle, the 3 kings of that genre are Devil Dice, Kula World and Kurushi (IQ in American).

And get Omega Boost as well.

Crash Team Racing
Wip3out

(I think Wip3out is one of the only PSOne games that holds up visually till this day)

Get the Driver games. Also, if you don't mind getting games ported from PC you might enjoy Red Alert and Quake II. I enjoyed them both a lot.

Legacy of Cain: Blood Omen and Soul Reaver.

Silent hill and legend of dragoon.

Tekken 3 and Bloody Roar 3

Motor Toon Gran Prix

Ape Escape
Digimon World 1
Nascar Rumble
Darkstalkers
Tekken 2 & 3
Parappa The Rapper
Twisted Metal
Medievil
The Legend Of Dragoon
Alundra
Tomba!
Lomax

Here are someday that haven't been mentioned:

Vanguard Bandits
Rhapsody A Musical Adventure
Brave Fencer Musashi
Evil Zone
Thrill Kill

So you want to collect them! Then I recommend you use this site. http://videogames.pricecharting.com/console/playstation?sort-by=highest-price

It is useful if you want to collect since it gives you the approximate price of the games you want to get. Good luck! Games like Suikoden 2 are about 80 dollars+ used. It also gives you link to the sites where you can buy those games!