We discuss custom time-tagging instrumentation for high-speed single-photon metrology, focusing particularly on implementations that can tag and process detection events from multiple single-photon detectors with sub-nanosecond timing resolution and at detection rates above 100 MHz. The systems we present view the detector signal as if it were a serial data stream, tagging events according to the bit period in which a rising edge from the detector occurs. We achieve sub-nanosecond resolution with serial data receivers operating up to 10 Gb s(-1). Data processing bottlenecks are avoided with pipelined algorithms and controlled data flow implemented in field-programmable gate arrays.