Font-awesome, input type 'submit'

use button type="submit" instead of input

<button type="submit" class="btn btn-success">
    <i class="fa fa-arrow-circle-right fa-lg"></i> Next
</button>

for Font Awesome 3.2.0 use

<button type="submit" class="btn btn-success">
    <i class="icon-circle-arrow-right icon-large"></i> Next
</button>

HTML

Since <input> element displays only value of value attribute, we have to manipulate only it:

<input type="submit" class="btn fa-input" value="&#xf043; Input">

I'm using  entity here, which corresponds to the U+F043, the Font Awesome's 'tint' symbol.

Then we have to style it to use the font:

.fa-input {
  font-family: FontAwesome, 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

Which will give us the tint symbol in Font Awesome and the other text in the appropriate font.

However, this control will not be pixel-perfect, so you might have to tweak it by yourself.