i loved iron mountain road, spearfish canyon, crazy horse/mount rushmore and the badlands. i didn't especially enjoy devil's tower, and won't go back this year but i think i'm in the minority with that one.

 

I second softail Chica. Basically all the Canyon roads are understandably nice. Vanocker Canyon and Nemo road provide a nice transition from Sturgis to Rapid City and the Harley Dealership if you feel so inclined. There are dozens of beautiful roads that very few who visit the rally ever see. Just turn left when everyone else is going straight.

You may also want to check out a little bar in a town of 12, Rochford, that is known to a lot of the old school clubbers. Very cool place and no traffic on the way there. The photos on the walls are worth a million.

 

Sheridan Lake Road, one of the prettiest!!
Take that from some one that lives here...

 

If you are going out west I would recommend a side trip to ride the Chief Joseph Byway and Beartooth Highway.

To take in all the sites and stop at the scenic overlooks on this side trip I would recommend three days.
Day 1 from Sturgis over the Big Horn mountains to Greybull WY.
Day 2 Geeybull WY to Cody to Chief Joseph Byway to Bearthooth Highway into RedLodge MT
Day 3 Redlodge MT back to Sturgis.

Google Beartooth Highway to get all the info about it. It's an amazing ride going over the summit at almost 11,000 feet

Here's some videos
http://www.youtube.com/watch?v=40LMMwhCg3g

http://www.youtube.com/watch?v=4hlix..._order&list=UL

http://www.youtube.com/watch?v=RmTuP..._order&list=UL

Have Fun There.