I've always avoided Keychain, so I don't know whether you can dump it altogether once it's been set.
At least with the initial setup, with Tiger anyway, you don't need a password. Leaving the password box(es) empty prompts a warning, but if you ignore that, from then on a simple mouse click is the password. But that leaves you open to quick clicking malware OKs.
Passwords for some web sites that won't stick, such as Yahoo mail's and even those of some banks, will remain if you're running Firefox and the extension/bookmarklet Always Remember.
It works even with the very old OS 9 Mozilla browser that won't accept most extensions and no bookmarklets whatsoever, simply by bookmarking the Always Remember bookmarklet on the web site, and choosing it before entering the password. It's JavaScript. I've never tried the old-Mozilla method with Safari. I doubt it could work, though.