I know it's not the most helpful thing to spoon-feed sometimes, but I had needed a break from work.
Demo: http://jsfiddle.net/wesley_murch/SzHQZ/
Looks nice in FF4 and Chrome, IE falls back to decent looking (though you could fix it with PIE).
Here's the CSS I used, I got the gradient code from some random online generator so it might not be optimal. There's too much contrast as well compared to your image, so just fine tune it.
<button>
<span>
Sign in
</span>
</button>
button {
border:0;
padding:3px;
background:#735544;
background-image: -webkit-gradient(
linear,
left bottom,
left top,
color-stop(0.18, #271D1B),
color-stop(0.59, #735544)
);
background-image: -moz-linear-gradient(
center bottom,
#271D1B 18%,
#735544 59%
);
border-radius:8px;
-moz-border-radius:8px;
-webkit-border-radius:8px;
}
--- Needed this break to get markdown to behave...
button span {
display:block;
color:#fff;
font:900 18px arial;
text-transform:uppercase;
padding:.35em 1.3em;
background:#382B25;
background-image: -webkit-gradient(
linear,
left bottom,
left top,
color-stop(0.18, #382B25),
color-stop(0.59, #C2A489)
);
background-image: -moz-linear-gradient(
center bottom,
#382B25 18%,
#C2A489 59%
);
border-radius:4px;
-moz-border-radius:4px;
-webkit-border-radius:4px;
}