Lets not forgett other great Level-5 games like: Dark Cloud Dark Cloud 2 (aka Dark chronicle) and my own personal favourite Rogue galaxy for the PS2
Both Dark Cloud 2 and Rogue Galaxy have a nice cellshaded graphic that should speak to people who enjoyed this game. Its not as simulair as DQ8 but ROgue Galaxy is atleast a good runner up in the "games that inspired NNK" cathegory.
Waiting for Ni no kuni (PS3), Final Fantasy X HD (PS3), Metro Last Light (PS3)
Dragon Quest VI (DS) (two worlds and similar adventures) Dragon Quest V (DS) (has monster catching too and similar adventures) Dragon Quest Monsters Joker 1&2 (DS) Blue Dragon (Xbox 360) (similar world map and gameplay aside from the combat) Chrono Cross (PS1) ("another world")
I realize I'm in the immeasurably small minority, but I've tried every one of them, and none of them appealed to me. Dragon Quest 9 held my interest for longer than the rest, but it still wasn't for very long. I know 95% of anyone who's ever played a jrpg seems to claim Chrono Trigger as their favorite, but eh...just didn't care for it. I was more fond of Chrono Cross tbh, lol. I still rather enjoyed Ni No Kuni. I can see the similarities to the Dragon Quest titles, but they're not so similar that 'if you like this game, then you will definitely love ___' or anything.