my bro sold FFVII at a anime convention for $150 used. he said it didnt even last for 2 days on the shelf. FFVII also embarked a series of other games related to it so thats another reason the game is in high demand. there is also a misprinted version of the original black label game thats selling for about $10 more sometimes the same amount as a regular version. its just that one of the letters in the back got mixed up.
i have been selling ps1 games on ebay recently, theres definately a higher demand for them than any other games for older systems. here are some i sold some i have sold awhile back:
klonoa door to phantomile (sold it like around 5 years ago) - $80 used
intelligent qube - $70
silent hill sealed GH - $60
legend of mana sealed - $70
some of the games ive been watching for awhile now:
tactics ogre - around $60
silent hill original black label - $50 to $60
the lunar series - like around $40 to $150
final fantasy tactics - $40 to $60 (usually more if its not the GH)
tales of destiny - $60
suikoden 1 - $50
ddr: disney mix - $150!?
marvel vs. capcom 1 - $40 to $60 (this has gone up since i guess people found out EA made a deal with Marvel to release all their games for the future, canning the idea of a sequel (part 3) or even an anthology collection

Bust A Groove 1 or 2 (this game is by ENIX) - around $80 or more..
theres a few more i cant remember atm..
if you really want to see something unique, then check this out: last year i was browsing for ps1 games on ebay and i noticed that there was 1 particular MGS 1 game that was priced at a whopping $1000. i didnt understand why until i saw that the game was actually a misprint. heres a picture:
http://www.playstationmuseum.com/Miscellaneous/COLLECT/COLL07/
he was the one that one selling this. i watched it but it didnt sell, there was a similar version but GH which i think didnt sell as well.