[hat and beard]

The Tenderloin can actually be quite cool. There are alot of small ethnic neighborhoods within the Tenderloin which means there are a lot of excellent hole in the wall resturaunts. There are some pretty cool clubs there, as well (Hemlock Tavern). Just be careful. I've nearly been robbed there more than once.
Aquarius Records in the Mission and Amoeba Records in the Haight Ashbury area are not to be missed for record hunting. There are some other decent record stores and book stores in the Mission and Haight-Ashbury worth looking at.
I second the Clement Street area recommendation as well. There are sooooo many great resturaunts there.

I would also avoid Fisherman's Wharf at all costs. Tourist trapiest tourist trap there ever was.