Dissidia was a fun take on the Final Fantasy universe, adding all sorts of mad combat with characters from across the series on a couple of outings for the PSP, with the Duodecimal version selling over 500,000 in Japan, with a tasteful limited edition. I still have the review UMD for the first one somewhere, must give it a spin again.
Square is upping the ante for the next instalment with a full arcade game, which doesn't sound like it'll be particularly easy for a handheld conversion. Naturally, this new version features characters from the latest titles and is maxxed out on the graphics front. More info is coming in April,