The land i plan to build on has a slope facing south so i was planning a passive solar design tucked into the hill (earthship style on the cheap!). However, having looked at some of the ideas suggested here that seems like it may not be the ideal way. Help!
Secondly, I understand where you are right now. Passive solar is a wonderful thing, but there are a lot of different ways to go about doing it. There is nothing wrong with using that south-facing slope and the sun to heat your home. Where many people get trapped is designing a house which defies the geometry of the hill it's built into and have to deal with water issues and ventilation issues.
Personally I am a big fan of the Mike Oehler earth integrated designs as they use mostly indigenous materials and leave your living space as natural and rustic as possible. Plus, I'm not a big fan of pounding soil into old tires with a sledgehammer (as in earthship).
Oehler's design uses the slope of the land in such a way that you take the pressure from the uphill side of the home and let light in that way, while still retaining the benefits of underground. You will find a lot of cool ideas in here. Be sure to read Paul's WOFATI article, as that has a lot of interesting ideas integrated into one and kind of lets you view some of the options side-by-side.