good point genome! yah I've heard great things about the sigma primes as well, I actually chose the 50 1.4 canon version because of its lens flare, which was something I was specifically looking for, see JordanVoth's work on here, truly inspiring and the flare he gets out of this lens is amazing.
Dan, $800 for the 50 1.4 there?!?! Holy crap thats ridiculous. I picked it up brand new for $377 with tax (I bought in a store that matched B&H so no shipping costs). Check it out, I haven't really used it for any specific head-shots so I do not know how sharp it is in comparison to the 15-85 which is one of the sharpest lenses i've EVER used, but hopefully soon!