I guess what sounds good to one person may not to the next, but I have not found anything on the free download sites that I would use. The only ones I have found that I consider good sounds (other than a few Fox Pro sounds, which are not MP3) are Johnny Stewart. You can buy the Johnny Stewart sounds in MP3 format on CD from several different places. I would rather have 3 or 4 really good sounds than have 100 in poor quality.
Having grown up on a farm, I have heard lots of real live rabbits and other animals in distress. Most of the sounds you find on the internet for download do not even come close to the real thing. That is why I prefer a mouth call for most of my predator calling. You can make them sound much more distressful than any electronic recording that you will find on the internet.