Safari has an option to remember passwords, it doesn't work on every site, but most sites it does. It will fill in the username and password when you visit the site, all you need to do is click "login"
firefox also has some good password management tools, but if you don't want to lose them I suggest third party software.
most people here would probably recommend 1password, as it stores all passwords, and integrates into your browsers and I believe even some applications as well.
I like "steel" personally. It stores my info in a password protected (and encrypted) file, which I can open when I want. The passwords aren't one-click away from anyone using my computer. I can remember most things, and I let Sarafi remember some for me initially, but I always have that file for reference.