What's the easiest way to automate logging into a website?

There are commercial tools that do this very well. Each is a drop in the bucket if you depend on them, but are in the $25-35 range since they do many things other than just this one single task. 1Password might be better at a single key command to fill in both a username and password, but TextExpander is also very awesome at what it does and might be more useful in the long run if you don't need a password generation/wallet replacement.

• 1Password - from where I sit, the best tool for improving web form management securely. It integrates with just about every browser and it very actively being developed.
• TextExpander for Mac - also, the best of class for taking short snippets and expanding them no matter what app you need the typing assistance.

They do different things and are both on the App Store. Check the developer web sites to see if they have free demo versions - especially if you don't feel you will need them or have concerns about buying without seeing them.

The Lastpass plugin is configurable to autologin to sites. It operates a freemium model, so all of the basic features are free (including autologin).