Name is rather self explanatory. Info about the production aspects of US paper money. The main part of the site is the serial number tables, which list data from the monthly BEP reports, going all the way back to the 1970's. There are several other useful articles on the site as well.

On the topic of old-style bills, I really like the way they look compared to the first generation of new designs (with that huge portrait off to the left) However, I do like the 'color background' $10, $20 and $50 designs.
Here is an explanation of why the distinction between FRBs matters. They are not just glorified distribution centers.

Where's George? Collector's Forum Excelsior (his screen name) provided me with the answer to the FRB question on an older incarnation of this forum.
The Signature Combinations On US Paper Money

Every U.S. dollar bill has the signatures of the Treasurer and of the Secretary of the Treasury. This page lists what those combos were at various points in time.