Join the Castle Coalition
If you want to do something about eminent domain abuse, join the Castle Coalition, created by the Institute for Justice to help victims of eminent domain abuse.
This group has had great success, and obviously, there's a lot more to be done.
Eugene Volokh explains:
Kelo was litigated by the Institute of Justice, a first-rate libertarian public interest law firm; I think it's much to their credit that they could get even 4 votes -- the last case that squarely considered this issue, Hawaii Housing Authority v. Midkiff (1984), was unanimous, and Justice O'Connor and Chief Justice Rehnquist were on the side of the government there. I don't agree with them entirely as to Kelo, but I still very much respect their work, in this case and in others.
IJ has also been very successful fighting battles in lower courts, either under state constitutions or getting policies struck down under the "rational basis" test, the same test that now applies in the eminent domain "public use" analysis. Constitutional scholars may tell you that rational basis cases are virtually impossible to win (at least unless the courts conclude that the law improperly discriminates against some group, almost never an economically defined group). But IJ somehow manages to win them.
Finally, the IJ people are masters at using their cases to marshal public opinion. That often helps them pressure the government to change its policy even without a final decision in litigation. And it also helps them use cases, whether they win them or lose them, to build pro-economic-liberty sentiment generally; they're especially good at showing how economic liberty helps the little guy.