AKG D30 "The Zep" mic, mounted to capture Mike's kick drum

The world's first dynamic cardioid mic, made in the late 1950s-early 60s. A D30 is basically two D12s with 4 selectable pickup patterns and switchable bass roll-off at 50Hz.
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Mentioned in Kerry's first "Tech Tuesday" blog post on 2009/09/15 as part of a run-down of mics used to capture Mike's drum sound:

On the outside of the kick and about 4" from drum head we are using 2 microphones a Beyer M88 TG (this is nice for that super tight low end punch) and an AKG D30 (This is the microphone that was used to get that huge kick drum sound used on many Led Zeppelin recordings. We call it of course the "Zep Mic".)