Cherubae's Terranigma Info Page
Contains weapon/item/skill/enemy lists, magirock locations, experience chart, and fan fics.

TerraEarth
Probably the best around for info and media on Soul Blazer, Illusion of Gaia, and Terranigma.

Ulan Shad's Terranigma Maps
Has some maps and sprite rips.  Hasn't been updated in a long while.