HTTPFox is an interesting Firefox extension for monitoring the HTTP traffic, obviously inspired by the IE-only commercial HttpWatch.
HTTPFox shows some stuff that are missing from Firebug's Net Panel, such as requests for favicons and such. There's also a little search box that lets you filter the list of components. Pretty cool too is the ability to select and copy the list of components.
Funny today I played with a little export feature in the Net Panel, logged here, demo here.