PwdHash generates theft-resistant passwords for a website based on a master password you specify and the website's URI. A Firefox extension is available to automate the process, but no similar solution for Safari or other browsers exist.
SuperGenPass is a bookmarklet that accomplishes the same task but with a different password generation algorithm. It has a simple and effective interface and is compatible with most browsers.
SuperPwdHash, as you might have already guessed, is a bookmarklet based on SuperGenPass but generates passwords using PwdHash's algorithm. Tested working on Firefox 3.0.1, Safari 3.1.2, and the iPhone. Simply bookmark the link below and use it when you need a good password.
IE6 users please bookmark this link instead: SuperPwdHash