As mentioned at MAX 2008, Flex Builder 4 will have a built in network monitor so that you can watch what's going on behind the scenes as your client interacts with back-end servers.
But... until then, a tool you definitely need to have (even when FB4 becomes available) is a good traffic analyzer. The two popular ones for use with Flex are ServiceCapture and Charles Web Debug Proxy.
These tools are lifesavers, and can save you an enormous amount of time when trying to figure communication/integration issues.
Kevin Langdon has now released a major update to his ServiceCapture tool which has a slew of nifty enhancements. Here's a snippet:
Save and Restore Sessions
A full session's data can now be saved to a portable file. This allows you to open up a previous session from any computer. It is the perfect way to prove to a remote team member that you are in fact seeing some unwanted server responses.
Firefox Extension to Automatically Handle Proxy Settings
Now with a very simple installation, you can say goodbye to starting and stopping Firefox while working in ServiceCapture.
See Trace Output from Flash Player
If you have the flash debug player installed, ServiceCapture will now display all trace() calls inside it's UI.
Map URLs to Local Directories
You can now map a segment of a URL to a local directory. This allows you to mimic a complete static website from your hard drive with no local server and the whole time your browser still thinks it's hitting production servers.
Resend/Test any HTTP request
You can now select resend any HTTP request and view the results. This allows you to isolate and test a specific service call. Gone are the days of signing in and recreating 33 steps to test one call back to the server.
Include/Exclude Based on URL Regular Expressions
Tired of seeing all those request for files you don't care about? You can now exclude or include requests based on any part of the URL, domain, extension, or query string.
Monitor ANY Log File
You can now setup ServiceCapture to point at any text-based log file on your system and it will display logging inside the UI with the other events and network traffic. This is great for watching an HTTP Server error file for any issues that might be related to your browser's requests.
Images Displayed in Response Area
A new tab was added to the Response area to allow you to view any image that is served back to your client.
For more information visit www.kevinlangdon.com.