Got fired from my job. What do I tell future employers when applying for new job?

I was fired from my  job a few weeks ago and recently forwarded a resume to a recruiter. He noticed I was terminated from my job and said they might not be able to help me because I was fired. I'm wondering if anybody has some good suggestions on what I could say instead of saying I was terminated if a future employer wants to know why I'm no longer at my company. I was thinking of saying I was downsized but am not sure if a potential new employer would be able to find out I'm not being honest.