This is a really simple trick but one I only learned recently after using Webflow for a couple of years.
If for some reason you need a form element (i.e. input field, textarea, checkbox, radio button, dropdown select, button) without wanting to add a full form to your page - you can drag in individual form elements by holding ALT + dragging the element onto the canvas.
Tis as simple as that!
THIS IS NO LONGER WORKING - unfortunately, it was deprecated recently.