Here's a new theory that does without Dark Matter:
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> http://www.physorg.com/news/2011-08-dark-illusion-quantum-vacuum.html
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> It postulates that antimatter and matter have opposite "gravitational charges" analogous to positive and negative electricity. 
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> I like the idea. It could explain a lot of things. 
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> On the other hand it could be totally wrong of course. 
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> It can be tested, so it's good science.-Thanks for noting this. I had seen it but was disturbed by the last paragraph which had many factors to negate the theory:-'In the end, Hajdukovic notes that much more work needs to be done before claiming that this possibility is the correct one. For one thing, the rotational curves of galaxies are not the only phenomenon that can be explained by dark matter. Observations of the cosmic microwave background, gravitational lensing, supernovae, and other data can also be better explained by the existence of dark matter than without it. With many scientists currently investigating dark matter and other alternatives, Hajdukovic hopes that new answers will continue to be discovered.'