The Beastmaster is a job class that is useful in many subtle ways. This class allows you to control and capture monsters. These abilities may not seem that important, and are often time consuming, but you'll need them in order to aquire some of the rarer Blue Magics and items in the game. The Trainers themselves are moderately powerful, but cannot equip the stongest weapons, instead preferring the whip or bute. And they, of course, are not very skilled in magic. A useful ally in certain situations, it is best to learn the 'Cntrl' ability quickly and then switch to another, more powerful class.
The Geomancer is another class which you'll be using quite a bit in order to succeed in certain situations. Their most notable and useful abilities include finding trap holes in the floor for you and giving you the ability to walk unscathed across floors which would normally cause damage (lava pits come to mind). The Geomancer is considered a magic user, for those of you who are in the dark. There is no need to buy, or aquire through side quests, the spells for them. Instead, they will use the magic of the Earth. This means they will cast a random spell chosen from a selection of four or so spells depending upon what kind of ground they are fighting on. For example, their spell selection will differ drastically when fighting in the mountains as compared to, say, the open field. These Earth Magicks can be quite powerful, but, since they are randomly chosen, they can be unpredictable (not a very nice option in battles that count);
The Ninja is, of course, one of the best jobs that there is! They have pretty much average stats all across the board, except for a high speed rating, but they more than make up for that with their other abilities. The one that stands out the most is the ability to equip two swords, which, when leaned after many battles, can be transferred to any other class. The Ninja can also throw weapons and stars and scrolls containing certain elemental runes inscribed upon them (LigtningSkil, FireSkill, etc.). Also, given the Ninja's speed, they have other abilities which will increase your chances for getting the first attack, being able to quickly escape nasty battles, and causing the enemy to miss their targets. The Ninja class has access to some of the strongest (and coolest) weapons in the game. Definitely an excellent job!