> I have been wishing there was a JPEG equivalent with an alpha channel for like forever.

JPEG 2000 works in Safari. JPEG XR in IE. A gracefully-degrading JPEG XT is in the works: http://www.jpeg.org/jpegxt/index.html

Lossy PNG with alpha works in all browsers: http://pngquant.org (not equivalent in compression ratios, but still 4 times better than normal PNG).