The way HTML input fields are rendered varies even among modern browsers. Internet Explorer is notorious for not vertically-aligning input text if you don't use the right CSS, but even Chrome and Firefox differ in certain circumstances. Text might be vertically aligned in one browser, but then in another might look like this:

CSS Fix

To get your input fields to render consistently across all browsers, with pixel-perfect height and vertically-centered text, you need to use both height and line-height, and avoid vertical padding. You'll also want to supply your own horizontal padding. Here is an example:

.input {
height: 35px;
padding: 0 6px;
line-height: 35px;
}
This is tested all the way back to Internet Explorer 6 and works consistently.

More Details

The reason you need both height and line-height is because height controls the height of the input field, while line-height controls the height of the text inside. If the line-height is too large relative to the input field height, the text will be pushed outside of the field.

You need horizontal padding so the text doesn't sit directly against the ends of the input field.