I don't know my language archaeology but what about:

• Taint mode.
• tie - alternative implementation of builtin types.
• floating point version numbers (ok, not so good).
• pick your delimiters qq//, q//, qw//, qx//, m//, s///...
• sigils, not just for evaluating/interpolating but as a different namespace.

I agree with the posts above, that Perl's value is in providing a rich choice of features from diverse languages and combining them in a way to easily get things done.

I think Perl6 will probably rate as truly innovative, in a number of ways. Grammar/regex integration and junctions are my picks.

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