CME & CBOT pits
I went to Chicago in october last year - the CME and CBOT both having viewing galleries, but from what I gather they are no longer open to the general public due to security concerns - you cant just roll up and gain access, although you may be able to arrange something in advance if you telephone.
your best bet would be to get in touch with your broker or somebody with ties to the floor if you broke in the US, if you can get someone to take you onto the floor and tour you round it, its a lot more interesting being in the thick of the action!
I had the opportunity to get onto the floors at both exchanges and it was truly a fascinating experience!
CBOT floor housing the bonds and dow pit amongst others, is just immense! the room itself is a sight to behold, four storeys high walls covered in dealer boards... sadly, the action on the floor seemed to be light. The only pit that seemed to be truly thriving was the Eurodollar pit upstairs at the CME - nicknamed the "bananaboat" by locals, the pit is a longboat shape raised up at either end and on the sides crammed with maybe 6-700 traders. Noise levels were incredible!
The group I was with also had the chance to engage in a mock trading session with the locals just after the session closed - also an experience! I ended up short 80 cts without quite understanding how at the end of that little run.