desktop cards. There is no such animal.
Hybrid crossfire - was a term to describe a combination of IGP and some discrete video cards. Basically all support for it is gone. It didn't return much performance and it had major stability problems.
Hybrid sli- would be nvidia products and they employed this like above in some notebooks. http://www.nvidia.com/object/hybrid_sli.html
You can't sli different Nvidia cards. In some cases 9800 1gb could be matched up with 512mb 9800. But not different models.