Genuine Fractals is a plugin for Photoshop that does lossless saving in a .stn file format. The format is actually a series of fractal type formulas so the image can be resized and it looks great. It also compresses the file size quite a bit. Its mostly use for large images, 10 meg +.
Unfortunately it looks like the LE version is no longer available, so you only have a 30 day trial and the full version is $199. I got the LE version years ago for $25, ver 2.0, they are up to 4.0 now.
For $50 it would be a great plugin to have if you make huge files or would like to do a lot of resizing. For $199, it seems way over priced unless you are making money with it, or you have piles of cash. http://www.ononesoftware.com/detail.php?prodLine_id=2