[storborg]

Just to toss out a few ideas: software defined radio, high-throughput DSP (like audio processing or machine vision), MITMing of fast protocols, packet inspection, CPU emulation.

[zmanian]

I found http://opencores.org/projects nothing is a killer app right now.

At work I use an FPGA as async real time controller. Not sure what utility that would have if not connected to specialized hardware.