Something I meant to mention awhile back: Fiddler, my favorite HTTP debugger that I've mentioned in the past, released version 1.0 over the summer. (It's now up to 1.0.1).

Fiddler has always been one of the better tools for doing HTTP inspection - I personally think it's faster and easier to use than Paros and has always been better with dealing with NTLM/Kerberos authentication. And, as the name suggests, you can "fiddle" with the requests and responses. This latest version also includes support for HTTPS inspection, no small feat in itself.