I was recently "laid off" from my place of employment... the reason given was they needed to downsize due to economic difficulties. I believed then, and now know that it was due to lies and half truths from a co-worker.
I've received phone calls from past and present employees and coworkers who said this person was making false statements about me. The company that needed to downsize, has miraculously recovered and is now searching for someone to occupy the position I once held.
I am angry, but most of all hurt. I've been in my profession for 15 years and have made and kept many friends along the way. I've been a hardworking and loyal employee and feel that I should have been given the benefit of the doubt by my employer, which actually disturbs me more.
What do I have the right to do?
I want them both to know, that I am aware and informed, and that what transpired was unethical and borderline illegal.
Your guidance would be greatly appreciated.

Consult an attorney. You will need to first get proof of what this co worker said. You will also need proof or at least enough evidence to convince a court that the statements were the cause of your losing your job.

If you can do that, then you may win a case of slander against the co-worker.