[FLT8]

- Error correcting codes (viterbi, reed/Solomon, ...)

- cryptography in general

- data compression

- a lot of DSP stuff is pretty magical in it's various applications - digital filtering, modulation/demodulation, recovery of weak signals in noisy environments, beam-forming etc

There's a lot of really amazing, largely mathematical, foundation work that we now tend to take for granted and without which we'd be back in the relative dark ages.