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.
There's much more about the book via http://geekatlas.com/