iOS: Debugging Web Services

Some useful tools & tips for debugging iOS apps which connect to web services:

Debugging in the iPhone Simulator

Wireshark - free, open source app.
Charles Web Debugging Proxy - paid app, with free trial. Supports SSL connections.

Debugging On-Device

Paros Proxy - free, open source app. In Paros, go to Tools -> Options… select the Local Proxy option. Enter your Mac's IP address and leave the port at 8080. On your iOS device, go to Settings -> Wi-Fi, select the same network as your Mac and tap the blue button. Set HTTP Proxy to Manual and enter your Mac's IP address under Server and 8080 for the Port.
Charles Web Debugging Proxy - On your iOS device, go to Settings -> Wi-Fi, select the same network as your Mac and tap the blue button. Set HTTP Proxy to Manual and enter your Mac's IP address under Server and 8888 for the Port.