How to submit a form when the return key is pressed?

IMO, this is the cleanest answer:

<form action="" method="get">
  Name: <input type="text" name="name"/><br/>
  Pwd: <input type="password" name="password"/><br/>
  <div class="yourCustomDiv"/>
  <input type="submit" style="display:none"/>
</form>

Better yet, if you are using javascript to submit the form using the custom div, you should also use javascript to create it, and to set the display:none style on the button. This way users with javascript disabled will still see the submit button and can click on it.

It has been noted that display:none will cause IE to ignore the input. I created a new JSFiddle example that starts as a standard form, and uses progressive enhancement to hide the submit and create the new div. I did use the CSS styling from StriplingWarrior.

I tried various javascript/jQuery-based strategies, but I kept having issues. The latest issue to arise involved accidental submission when the user uses the enter key to select from the browser's built-in auto-complete list. I finally switched to this strategy, which seems to work on all the browsers my company supports:

<div class="hidden-submit"><input type="submit" tabindex="-1"/></div>

.hidden-submit {
    border: 0 none;
    height: 0;
    width: 0;
    padding: 0;
    margin: 0;
    overflow: hidden;
}

This is similar to the currently-accepted answer by Chris Marasti-Georg, but by avoiding display: none, it appears to work correctly on all browsers.

Update

I edited the code above to include a negative tabindex so it doesn't capture the tab key. While this technically won't validate in HTML 4, the HTML5 spec includes language to make it work the way most browsers were already implementing it anyway.

To submit the form when the enter key is pressed create a javascript function along these lines.

function checkSubmit(e) {
   if(e && e.keyCode == 13) {
      document.forms[0].submit();
   }
}

Then add the event to whatever scope you need eg on the div tag:

<div onKeyPress="return checkSubmit(event)"/>

This is also the default behaviour of Internet Explorer 7 anyway though (probably earlier versions as well).