Trail info can be had already from our local USFS office. They've got free maps to the Centennial Trail (over 100 miles of singletrack through the heart of the Hills), Deerfield and Deerfield Lake Loop trails, Crow Peak, Big Hill, Silver City and other worthy riding.
Don't forget the Mickelson Trail that covers 100+ miles of Rails to Trails riding on the historic rail grades built many years ago to extract riches of gold from them thar Hills!

Bicycle Lanes vs. Wide Outside Lanes
Black Hills Mountain Bike Association
Skyline Drive Master Plan (4 MB .pdf file)
M Hill Trails (5 MB .pdf file)