I'll start with console type.
If you like Kingdom Hearts you might like KH: Chain of Memories. Though it's for GBA it's supposed to be pretty good. There is a new PS2 version of it called KH: Re: Chain of Memories. I've bought it but I want to finish KH first.
There's this game called Dual Hearts (PS2) that came out around the same time KH. It's little known, but that's because it came out under the shadow of the bigger hyped KH. Though I've never played it... it's supposed to be pretty good and I'd like to try it.
Dark Cloud (PS2) is a pretty good game. Not my favorite but it's fun enough. Dark Cloud 2 (PS2) is supposed to be much better. If I recall correctly, they're both cheap.
Pretty much any FF is good. The only one I can think of that I have a problem with is FFXII. It's license point system thing is really stupid. You'll get license points so damn fast they're no point in having the license board! Other than that it's pretty cool. If you go to GameFAQs there's a for-fun guide (LINK) that can explain ways to kinda give your characters "classes". I've not tried it yet but I bet it makes the license point thing better to deal with. It's supposed to be harder than playing normally however.
I've played Super Mario RPG, Paper Mario, Paper Mario: TTYD, and Mario & Luigi Superstar Saga. They're all cool. I wouldn't see why the newer Mario RPG series games for DS and Wii would be any different.
There is a line of games called "Megaman: Battle Network" for GBA and the ones I've played from it are pretty cool. There is also a slight spinoff for DS that's pretty much the same thing but a little bit different. They're called "Megaman: Starforce".
There is also a line of games called "Dragon Warrior". The original is for the NES but I think everything after that is for GBC (Maybe even GB), GBA, and DS. I haven't played any of them much but... there is a spinoff "Dragon Warrior: Monsters" which puts you in the role of a monster master that recruits and breeds monsters similar to Pokemon. I've played those more than the normal Dragon Warriors however. By the way, I've played the Pokemon series a bit and it's pretty good.
Golden Sun for GBA is a nice game. So is it's sequel Golden Sun: Lost Age, also for GBA. I like them.
I've played Monster Rancher 4 for PS2 and I like it. Not my fav but it's fun.
You can't forget about Chrono Trigger and Chrono Cross! I assume you've already played Chrono Trigger, but you should play Chrono Cross too!
Drakengard for Ps2 is an interesting one. It's a hack and slash with alot of RPG elements in it. It's fun... it gets a little old after while though. You should try it though.
I can't think of any more console types I have...
Moving on to PC types.
I don't know much about retail MMORPGs so I won't bother with the likes of WoW and such.
EUO looks pretty cool. It's a free graphical MUD that is based off the Ultima series. I haven't played it much, but it looks to be pretty fun. There's also one similar called Secret of Mirage. I haven't played it but it looks like it might be fun as well.
I've dipped into Text MUDs a bit and I've found Achaea to my liking. I've played a couple others a little bit but I like Achaea the best. You could try Aardwolf and Discworld too. They look nice and are the only ones rated higher on TopMUDSites.com.
You could always try some other rogue-likes besides Nethack. ADOM looks to be a cool one. There's even one modeled after DOOM (DOOM: the Rogue-like). There's a bunch more but those are the ones that get my attention.
I can't think of anything else...
It's a good idea to check out alot of reviews. It's boring, but just go to GameFAQs.com and go down the list of RPGs and you might find one. I'd recommend GameFAQs to anyone who wants cheats or reviews. It's a good game site.
EDIT: Sorry man. I mentioned some multi-player games anyway. I didn't see your last post. I was busy writin this big book