I tried to make a good looking Sign In form. Hope this helps you. Here we go:

New stylish sign in form using CSS3 and HTL5.

 

The html:

    <div style="margin-leftauto;margin-right:auto;">
        <div class="bubble">
            <h2>Sign in</h2>
            <div class="loginFormafter"></div>
            <form class="loginForm" name="loginForm">
                <fieldset>
                    <label>Username</label>
                    <input type="text" name="username" required="required" placeholder="Enter your user name" style="margin-left: 20px;" />
                    <label>Password</label>
                    <input type="password" name="password" required="required" placeholder="Enter your password" style="margin-left: 20px;"/>
                    <input type="submit" value="Sign In" style="width: 100px;" />
                </fieldset>
            </form><br/>
       </div>
    </div>

And the css:

body,div,h1,form,fieldset,input,textarea {
    border: 0;
}
body {
    background: #afafaf;
    font-family: sans-serif;
}
label {
    float: left;
    margin: 11px 10px 0px 0px;
    width: 95px;
    text-align: right;
    font-size: 16px;
    color: #1f6474;
    font-weight:bold;
    font-family: 'Segoe UI Light', 'Segoe UI', Arial, Helvetica, sans-serif;;
}
input[type=text],input[type=password]{
    width: 250px;
    height: 25px;
    padding: 5px 10px 5px 10px;
    margin: 0 0 5px 0;
    background: #fff;
    border-radius: 5px;
    -moz-border-radius: 5px;
    -webkit-border-radius: 5px;
    font-family: sans-serif;
    font-size: 12px;
    color: #000;
    border: 1px solid #82ccdd;
}
.placeholder {
    color: #123a44;
    font-size:12px;
}
input[type=text]::-webkit-input-placeholder,input[type=password]::-webkit-input-placeholder{
    color: #123a44;
    font-size:12px;
}
input[type=text]:-moz-placeholder,input[type=password]:-moz-placeholder {
    color: #123a44;
    font-size:12px;
}
input[type=text]:focus,input[type=password]:focus {
    border: solid #1f6474 1px;
}
input[type=submit]{
    height: 35px;
    float: right;
    display: inline-block;
    outline: none;
    cursor: pointer;
    text-transform: capitalize;
    text-align: center;
    text-decoration: none;
    font: 14px/100% Arial, Helvetica, sans-serif;
    padding: .5em 2em .55em;
    text-shadow: 0 1px 1px rgba(0, 0, 0, .3);
    -webkit-border-radius: 5px;
    -moz-border-radius: 5px;
    border-radius: 5px;
    -webkit-box-shadow: 0 1px 2px rgba(0, 0, 0, .2);
    -moz-box-shadow: 0 1px 2px rgba(0, 0, 0, .2);
    box-shadow: 0 1px 2px rgba(0, 0, 0, .2);
    margin-right: 10px;
    margin-top:10px;
    color: #333;
    border: 1px solid #777;
    background: #ddd;
    background: -webkit-gradient(linear, left top, left bottom, from(#fff), to(#ddd));
    background: -moz-linear-gradient(top, #fff, #ddd);
    background-image: -webkit-linear-gradient(top, #fff, #ddd);
    background-image: -ms-linear-gradient(top, #fff, #ddd);
    background-image: -o-linear-gradient(top, #fff, #ddd);
    background-image: linear-gradient(top, #fff, #ddd);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorStr='#ffffff', EndColorStr='#dddddd');
}
input[type=submit]:HOVER{
    background-color: #ddd;
    background-image: -webkit-gradient(linear, left top, left bottom, from(#eee), to(#ccc));
    background-image: -webkit-linear-gradient(top, #eee, #ccc);
    background-image: -moz-linear-gradient(top, #eee, #ccc);
    background-image: -ms-linear-gradient(top, #eee, #ccc);
    background-image: -o-linear-gradient(top, #eee, #ccc);
    background-image: linear-gradient(top, #eee, #ccc);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorStr='#eeeeee', EndColorStr='#cccccc');
    text-decoration: none;
}
.bubble {
    background: #fff;
    clear: both;
    margin: 0px auto;
    width: 350px;
    position: relative;
    /*rounded corners and box shadows*/
    -moz-border-radius: 5px;
    -moz-box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    -khtml-border-radius: 5px;
    -khtml-box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    -webkit-border-radius: 5px;
    -webkit-box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    border-radius: 5px;
    box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    overflow: visible;
}
.loginForm{
    margin-bottom:10px;
    background-color: #eaeaea;
    filter: progid:DXImageTransform.Microsoft.gradient(startColorStr='#eeeeee', EndColorStr='#cccccc');
    width: 300px;
    position: relative;
    z-index: 2;
    -moz-box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.55);
    -khtml-box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.55);
    -webkit-box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.55);
    box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.55);
    height:200px;
    left: -16px;
}
.loginFormafter {
    position: relative;
    height: 0;
    width: 0;
    left: -16px;
    top: 0px;
    border-width: 5px 8px;
    border-style: solid;
    border-color: transparent #555 #555 transparent;
    z-index: 1;
}
.bubble h2 {
    font-size: 30px;
    color: #123a44;
    text-shadow: 1px 1px 2px rgba(0, 0, 0, 0.2);
    border-bottom:solid 2px #82ccdd;
    width:90%;
    margin-left:auto;
    margin-right:auto;
    font-family: 'Segoe UI Light', 'Segoe UI', Arial, Helvetica, sans-serif;;
    padding-bottom: 5px;
    font-weight:lighter;
}

• CSS
• Java Script