Rice is the one person one potential candidate that I know would lose to Clinton. You and I both know that Clinton is a liar, but the stated political views of the two women are actually quite similiar. Rice is pro-choice, so she would lose quite a bit of the conservative vote. Plus, she's never held elected office.
Giuliani would most likely beat Clinton in a national race, but it would be close. Again, a lot of conservatives would stay home. He's pro-choice, pro gay marriage, and pro gun control. Either candidate might be acceptable for a socially liberal, moderate Republican, but neither is the type of candidate that anybody who frequents this website should be endorsing.