Actually, to their credit it looks like Starwood have changed the way they are displaying the resort fee when booking on spg.com. It's now clearly showing the resort fee and the tax on the resort fee, both on the screen where you select your room type, as well as in the "Rate Information" section of the next page.

Still not ideal, but not as hidden as it used to be (those that remember when Planet Hollywood introduced resort fees will know what I mean - it was originally not displayed at all, and when it was added it was hidden away in the fine print)