There have been no changes to Media Mail. It should show up in the "Economy" services section.
eBay has been trying to crack down on abuse of MM, so they might not be showing it if you're listing in a category that isn't usually eligible (e.g., listing a book about antiques in Antiques rather than in Books).
If you can't find it, then just choose flat rate shipping (rather than calculated), offer generic "Economy shipping" service, then look up the price in one of these resources below, based on package weight, to enter as your shipping cost. (Or add it to the asking price and offer free shipping.)
http://pe.usps.com/cpim/ftp/manuals/dmm300/notice123.pdf
http://www.ebay.com/shp/Calculator
