I can think of two things. First, as mentioned above, is certain regex executions. In particular, ones that quantify a compound submatch of varying length. I believe these are still done with C recursion, though I haven't looked lately.
Second, calls into XS routines that then call back into Perl.
There are probably a few others (recursive sorts? recursive runloop switches?) but by and large part of the initial design of Perl 5 was to be as stackless as practical (in the C-stackless sense). So all of Perl's stacks are really on the heap, and nearly all of the standard opcodes leave the C stack in the same state.
