Aluminum and composites (fiberglass, Kevlar or Graphite) would be good materials for chassis, subframe and suspension applications.  These "materials" are particularly attractive because of their low weight density, strength and corrosion resistance.  Aluminum has been used for structural components in aircraft airframes for decades.  Aluminum alloys are readily available and the techniques for design and manufacture are well understood.  Composite materials are also used extensively for airframes of advanced aircraft and spacecraft.  They are very strong and have engineered properties (stiffness, strength).  They are more expensive however.  Commercial supply for composite parts exists but they are more difficult to obtain because of the added engineering effort to use them.  They also contain resins that require testing to verify fatigue properties.

     Numerous material suppliers can be contacted on the web for detailed information.  Many composite material suppliers are willing to review component requirements with clients to make cost estimates.  Be sure to check the "Materials Engineers" forum.   

Thanks for the information Mike, I think I will have to check out the Materials Engineering Forum and composite suppliers as you suggest, because I will need to find out information regarding do's & don'ts of designing these types of parts, and how they are manufactured, to find out the best way of designing components in composites rather than in metals. For instance I will need to look at the layers of composites and the best ways to use their best properties to over come areas of high stress.
Kind Regards
Paul