I know that this thread has been answered, but I have tried a library that has worked great. I was using ASIHttpRequest before and the difference is big.
https://github.com/rs/SDWebImage
Also, if someone needs to Resize or Crop the remote images, and have the same features that SDWebImage provide, I have integrated SDWebImage library with UIImage+Resize library (by Trevor Harmon), and created an example project. I modified the code of SDWebImage to deal with transformations (crop, resize).
The project is public on https://github.com/toptierlabs/ImageCacheResize. Feel free to use it!