Hi Mac !,
Good idea! I bought a Tom Tom GO920 model from the States and it came fully loaded with US, Europe and Ausssie maps installed on a 4GB card ... really rapt in it!! You really need a GPS in LA!!! (I would offer to lend you mine but I cannot do without it when I visit Melb now .....)
Also a tip ... go on line to every US Mustang parts suppliers you can find and request a catalogue to be sent to the US address you are visiting. When you arrive, you will have heaps of reading and reference material to bring home!
Have a good trip!