How can I change the color as well as size of UIProgressBar in iPhone SDK
You could probably also hack one together using an image that looks like the progress bar at it's smallest size and then create a stretchable image with it.
UIImage *progressBarImg= [someImage stretchableImageWithLeftCapWidth:5.0 topCapHeight:0.0];
Then you could set the image as the backgroundImage for a disabled UIButton and animate the button width incrementally to indicate progress. I haven't tried this, but I think it would work.