Surge for Mac - Advanced Web Debugging Proxy for Mac & iOS
TrafficMonitor - TrafficMonitor is a network monitoring suspension window software in Windows.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
NetBalancer - NetBalancer is a Windows application for local network traffic control and monitoring.
HTTP Headers - HTTP Headers allows you to quickly see the HTTP header information for the current URL.
FreeMeter - Monitor network bandwidth (C#.NET 2k/XP+). Desktop and Systray graph.