I'm surprised no one has mentioned this yet, but Mac OS X has an application called "Keychain Access." Keychains store private keys, certificates, and arbitrary notes securely. I use one to store my passwords to all my e-mail and web accounts. They're encrypted using Triple DES.
Not only that, but it can generate passwords for you. Tell it how many characters you want, and whether the password should be memorable (comprised of dictionary words and a short string of numbers), letters and numbers, numbers only, something called "FIPS-181 compliant," or random. You can choose from the ones it generates from a pop-up menu, and if you don't like any of them, it can generate some more. Whatever password you choose, there's a gauge that tells you how strong it is.
I have to use it occasionally to look up a password to an infrequently visited web page. Entering my user password (that is, the one for my account on my computer) will unlock any one that is stored on the keychain.
Is it easy to use? Kind of, sort of; it takes a few seconds and more than a few mouse clicks to retrieve a password. Safari (perhaps Firefox as well, but I don't know) can be configured to remember your login information for a given page, and though it stores this information in the login keychain, the problem with Safari's implementation is that it works for some pages and not others, and doesn't require you to provide your user password--not exactly the most secure arrangement.
No one's ever compromised this scheme, as far as I know. Yet. Meanwhile, it works pretty well for me.