Wickard V Filburn - blew a hole in the constitution that opened the way for the imperial Federal Government.
http://en.wikipedia.org/wiki/Wickard_v._Filburn
That was pretty bad too. I still think Kelo may be worse, because it basically says everything belong to the King, and the King can take it any time he wants.
On the other hand, I’m not a legal scholar so I may be way off. Even if your choice stands, then Kelo is the worst in about half a century!
I dissent.
The main case that killed the Republic and our limited government was SANTA CLARA COUNTY V. SOUTHERN PACIFIC R. CO., 118 U. S. 394 (1886) where the Court Reporter illegally inserted an instruction from the Court to the Lawyers prior to the start of the trial. That addition to the Synopsis or Head-Note was then relied on by subsequent courts leading to the evisceration of the Rights of the People and marrying them to the Privileges of Corporations.
No where in the case at trial was any determination made that this statement is true. As there were other cases involved in the lower courts determining the reach of the 14th Amendment, the Justices did not want to muddy the field with an ancillary decision, since it had no bearing on the tax case before the court.
IANAL - YMMV
Here is a good site with details: ReclaimDemocracy.org.