Okay, so I promised a brief overview of the two plots I'm considering at the moment.
The first is along the lines of an extended character study.
One of the most interesting figures in fantasy tends to be, when it comes up, the lich. For the uninformed, a lich is a wizard/magician/etc. who uses his magic to preserve his own life as one of the undead. The lich is essentially trading the pleasures and frailties of life as a normal human for an essentially endless existence. Each lich has a reason for pursuing this change, though by far the most common ones given are "endless research" and "long-term planning." Liches hope to develop and study magic to perfection, and to enact some great plan that usually involves conquering large portions of the world -- someday. A rare few have other reasons, such as protecting a particular family line, some important item of magic, or to stand fast against the rise/return of some great evil.
So, all that said, my goal for this novel would be to follow a wizard and his thoughts, motives, and actions as he seeks out the secrets to transforming into a lich. He should, ideally, go from uncertain and a little squeamish to being much more willing to do vile things to succeed in this transformation. He must have a potent fear of death, and a reason for why he would forsake normal human relationships for the power and long unlife of such a hated creature as the lich.
The second plot idea is a story of a failed hero.
As in the other plot, the main character is a magic-user of some sort, though in this case his discipline is inherently foul and makes them ostracized. Magic power is something inherent to animal life, and so can only be regained once spent by eating meat. Now, on the surface, this isn't unpleasant at all, but far more power is gained from consuming the flesh of sapient creatures -- as in, humans -- than from those that are not sapient. While the vast majority of magic-users (what few exist) are by no means cannibals, just enough such people have cropped up to cause no end of problems for "legitimate" practitioners. The protagonist is using this disreputable magic because it's all he can really offer to The Cause, and things are moving so fast that he's the first magic-user found and pressed into service with the other heroes.
Yes, it follows the "party of adventurers" format to some extent. The heroes are rushing to reach the point where the barrier between worlds is thin, while your standard Evil Sorcerers' Cabal is seeking to open a gate to allow the olfen (think fairies, elves, and sidhe, except extremely violent and with a rapacious hunger for the "firmer" reality of this world) through en masse. The olfen have such power that just one is a great difficulty to fight, and an army of them could devastate the world.
The quest, however, is to essentially break the protagonist of his commitment to the preservation of the world. At the very end he will come to believe that the world is not worth saving, and because his magic is essential to stopping the spellwork of the Evil Sorcerers, the world is lost.