'Tcprstat is a free, open-source TCP analysis tool that watches network traffic and computes the delay between requests and responses. From this it derives response-time statistics and prints them out.' Computes percentiles, too

from Basho, via istvan. DTrace is becoming more compelling as a deep instrumentation/monitoring API -- I didn't realise disabled DTrace probes were virtually 0-overhead (a "2 NOOP instruction placeholder", apparently), that's nifty. Wonder if they've fixed the licensing mess, though