Have already been a fan of JpegMini and now comes TinyPNG. Many times it indeed happened that I converted a PNG to JPEG just to then minimize it using jpeg mini.
But what I liked the most about TinyPNG was:
Internet Explorer 6 normally ignores PNG transparency and displays a solid background colour. With TinyPNG the background becomes transparent again. No workarounds!
Link: http://tinypng.org/
