John, I' see that you have the Belgrade Tesla museum in your book -- but I think that even more interesting would be the visit to the village of Smiljan, Croatia. This is where Tesla was born, and there is a memorial center there -- http://www.mcnikolatesla.hr/ -- and you can find the place at http://6url.net/smiljan
I found Rutherfords Den in ChristChurch NZ quite an interesting diversion as well.. (And there's a delicious fudge shop around the corner - if that helps :P )
http://www.rutherfordsden.org.nz
From a glance at the site (haven't got the book yet) - I'm not sure if there were any entries from the southern hemisphere - if so - at least I could suggest one.
Any aussies reading have any suggestions from Australia? We have some good museums, (as well as Science Works, Discovery Center, etc) -- but I can't think of anything unique like that.. (The Snowy Hydro tour/scheme/workings were interesting - but i was pretty young then)
The only southern hemisphere location is the Parkes Radio Telescope in Australia. Would love to hear about more geeky places down under... http://geekatlas.com/ is the place to make suggestions.
Also, the Technical Museum in Zagreb has daily demonstrations of the Tesla's main inventions, including the 3 million volt transformer: http://www.mdc.hr/tehnicki/en/07-velikani/07-velikani-7.htm
Perhaps you could put some of those things to the next edition. :)