Here you can find a selection of eQSLs received, mainly from QSOs made on SOTA activations. 
Some of them exotic, others from well known SOTA activators and chasers.

QSL of Ian VK5CZ. The 1st S2S QSO VK-EA.
Probably one of the longest S2Ss in SOTA history.
(long path, 23457 km)
Very nice QSL from Paul VK5PAS confirming our S2S QSO!
One of my longest and hardest QSO on SOTA: ZL on 10Mhz