This CSS effectively hides the spin-button for webkit browsers (have tested it in Chrome 7.0.517.44 and Safari Version 5.0.2 (6533.18.5)):

input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
    /* display: none; <- Crashes Chrome on hover */
    -webkit-appearance: none;
    margin: 0; /* <-- Apparently some margin are still there even though it's hidden */
}

input[type=number] {
    -moz-appearance:textfield; /* Firefox */
}

<input type="number" step="0.01" />

You can always use the inspector (webkit, possibly Firebug for Firefox) to look for matched CSS properties for the elements you are interested in, look for Pseudo elements. This image shows results for an input element type="number":

Inspector for input type=number (Chrome)