edit/remove proxy settings

I'm looking for the proxy settings that persist throughout the system in Leopard, even after I have:

** removed them from my Location settings (in fact, I've removed all but one of the Location presets),
** made sure they're no longer in:
/Library/Preferences/SystemConfiguration/preferences.plist
** grep-ed for them in:
/Library/Preferences/com.apple.internet*.plist (but those look kind of binary/proprietary; I don't understand their contents)
** checked my .profile and made sure they were removed,
** tried 'networksetup -setwebproxystate Airport off',
** used 'unset' to unset them manually


... yet each time I fire up a new terminal window, and check for 'env|grep proxy', there they are. I'm not sure where else to look?

I've had proxy settings on my MacBook for a firewall at work, which have always given me trouble, since they use different IP ranges for internal and external connections (for example: IM would always work if I switched, but web would not). It would be great to be able to switch between proxy settings somehow via script, or some other way, quickly and cleanly.