I have been popping in to this board occasionally for a long time, but finally I have found a thread that has prompted me to post. I have been involved in using geophysics to "find" caves, but must point out that I am not a geophysicist (though I did work with some many years ago in the oil industry).
Unfortunately I cannot provide an example of a cave being entered after being "discovered" by geophysics, but I can give an example that comes pretty close. The work was carried out on the Laki Underground Expeditions (Iceland) in 2000 and 2001. Various geophysical techniques (magnetometry, resistivity and ground penetrating radar) were used over the up flow end of a lava tube cave called Stefanshellir. At the upflow limit is a short section of very large tube leading from a collapse entrance that suddenly ends at a complete lava seal.
The cave was very accurately surveyed (I seem to recall a station every 2m) and tied into a surface grid using differential GPS. the geophysical instruments were then used following this grid which had been accurately positioned with respect to the cave beneath (though the grid extended some distance beyond the known cave in all directions). The results are pretty unequivocal, the geophysical anomalies tie in excatly to the cave survey.
After the initial proving of the technique, the survey was extended up the lava flow, and appearsto show tha the lava seal is some 20m long and then a large cave passage continues for at leat 400m. The Icelandic Speleological Society were well enough convinced to start arranging for a drilling operation to enter the cave, but unfortunately a spate of politics has broken out which has put paid to this.
But, for some of the posters here I would suggest having a look at the expedition report (published by Bournemouth Uni, authored by Dr Chris Wood and available from Amazon or some caving club libraries) which contains plots of the raw data from the experiments. Even to a non-geophysicist the results are very clear indeed. There are a couple of poor quality pictures in the Shepton Mallet Caving Club Journal Series 10 No.10 as well which may be easier to get hold of.
I do need to point out however that conditions were almost perfect, flat surface topography with large passages only a few metres down. Also the magnetic technique which proved the most use is probably completely useless in Limestone caves.
Hope this is of interest in the debate,
Ed