<form action="" method="post">
      <label for="login-username">Username:</label>
      <input type="text" name="login_username" id="login-username" />
      <label for="login-password">Password:</label>
      <input type="password" name="login_password" id="login-password" />
      <div class="submit-block"> <span class="alignleft">
        <input name="" type="checkbox" value="" class="checkbox" />
        Remember me</span> <span class="alignright">
        <input type="submit" name="submit" id="login-submit" value="Login" class="sml-btn" />
        </span> 
      </div>
      <a href="#" class="lostpass">Lost your password or username?</a>
    </form>

<form action="" method="post">
      <label for="login-username">Username:</label>
      <input type="text" name="login_username" id="login-username" />
      <label for="login-password">Password:</label>
      <input type="password" name="login_password" id="login-password" />
      <div class="submit-block"> <span class="alignleft">
        <input name="" type="checkbox" value="" class="checkbox" />
        Remember me</span> <span class="alignright">
        <input type="submit" name="submit" id="login-submit" value="Login" class="sml-btn grey" />
        </span> 
      </div>
      <a href="#" class="lostpass">Lost your password or username?</a>
    </form>

http://bluzgraphics.com/phenomenon-wordpress

Phenomenon wordpress theme - Login box sample code

HTML