1Password is the most complete password manager that I have tried. This application has been around for quite some time and with every upgrade it always manages to add important and useful features to an already excellent application. In all honesty, 1Password has way too many features and I can't talk about them all here. I will tell you what I like the most about it.
The first thing that comes to mind when I think of the first time that I used 1Password was its design. I remember a very polished graphical user interface which was fast, responsive, and it had a lot of attention to detail. That hasn't changed, and the user interface is one of the best I have seen in an application like this.
1Password allows you to store passwords for websites, applications, and pretty much any sensitive information and lock it with a master password so that only you have access to it. The application has web browser integration and it supports the most popular browsers, like Safari and Firefox. It can automatically detect when you input passwords into sites and it will ask you to save that information. The next time you visit that website, 1Password will be able to log you in automatically. You can even launch your web browser and head straight to the login window from within 1Password.
The application also allows you to save what it calls "Identities". These are basically data bases with information about you, like name, address, phone number, etc. You can create as many as you want, and they can be used to fill up registration forms on the web automatically.
Perhaps my favorite feature in 1Password is the support for mobile apps. I used the iPhone version for a while to store secure notes and login information. The iPhone version can sync with the desktop version and get all your passwords over a wireless connection. And it works great.