When implementing/deploying and building all things BizTalk/Silverlight and related, there's going to be a time when you're needing to see what's on the wire.

I've currently found a few handy options:

1. FireFox's FireBug - brilliant! a plug-in straight from the browser environment. Deals only in Browser initiated traffic though.
   
   Gives great anaylsis on HTML page composition/scripts and dynamic content source - A MUST for any Silverlight work
   
2. Fiddler - sets itself up as a proxy that your browser requests through, once again, my browser has to initiate the calls.
3. Smart Sniff - smsniff - 48kb and this is a full blown packet anaylser giving access to all packets to/from NICs. - THIS by far is my choice!

Check them out folks - Smartsniff small enough to go on any memory key.

All free!