This quick tip is how to compress PNG image files even smaller than photoshop and still look visually great. An added bonus is the transparency works in IE6 (what?!! how.. that's crazy!!).
In previous posts I've talked about which image file format to use and work arounds to get IE6 to display transparency in PNG files
Over at tinypng.org you can upload up to 20 images to be processed (free) this will result in an indexed 8-bit PNG file with alpha transparency that is around 70% smaller file size.
Photoshop doesn't do this :( it just creates 24-bit PNGs (which are great but not as small as they can be).
Here's an example - the original png is 469KB and the tinypng is 138KB over 70% compressed can you tell the difference?
Original PNG: 469KB
Tiny PNG: 138KB (click to enlarge)