I used "Gator" to do this for a while until I discovered that it was "Spyware".  Now I've been using Roboform for a year or more.  It saves one heck of a lot of time by filling out forms for me automatically.  When a page comes up with a login and password box, or a form that needs to be filled out, Roboform pops up a box that asks you if you want it to fill out the form for you.  You click on "Fill in the form", or "Fill and Submit", and it fills in the form for you and even clicks the "Submit" button for you.

I would never be without it again!