Wordpress - Creating a table in the admin-style?

This is what I generally use:

<table class="widefat fixed" cellspacing="0">
    <thead>
    <tr>

            <th id="cb" class="manage-column column-cb check-column" scope="col"></th> // this column contains checkboxes
            <th id="columnname" class="manage-column column-columnname" scope="col"></th>
            <th id="columnname" class="manage-column column-columnname num" scope="col"></th> // "num" added because the column contains numbers

    </tr>
    </thead>

    <tfoot>
    <tr>

            <th class="manage-column column-cb check-column" scope="col"></th>
            <th class="manage-column column-columnname" scope="col"></th>
            <th class="manage-column column-columnname num" scope="col"></th>

    </tr>
    </tfoot>

    <tbody>
        <tr class="alternate">
            <th class="check-column" scope="row"></th>
            <td class="column-columnname"></td>
            <td class="column-columnname"></td>
        </tr>
        <tr>
            <th class="check-column" scope="row"></th>
            <td class="column-columnname"></td>
            <td class="column-columnname"></td>
        </tr>
        <tr class="alternate" valign="top"> // this row contains actions
            <th class="check-column" scope="row"></th>
            <td class="column-columnname">
                <div class="row-actions">
                    <span><a href="#">Action</a> |</span>
                    <span><a href="#">Action</a></span>
                </div>
            </td>
            <td class="column-columnname"></td>
        </tr>
        <tr valign="top"> // this row contains actions
            <th class="check-column" scope="row"></th>
            <td class="column-columnname">
                <div class="row-actions">
                    <span><a href="#">Action</a> |</span>
                    <span><a href="#">Action</a></span>
                </div>
            </td>
            <td class="column-columnname"></td>
        </tr>
    </tbody>
</table>

Hope that helps.

Use the Core API, not only its CSS

Normally you just use an instance of the WP_List_Table class.

Guides:

• More about it in the Codex here.
• Here's also a guide from WP Engineer - too much to copy it over.
• And another guide on Smashing Magazine online.

Benefits?

YES!

You can add pagination, search boxes, actions and whatever magic you can imagine (and are able to code).

Use this example (written as a plugin) to create your admin tables:

http://wordpress.org/extend/plugins/custom-list-table-example/

It uses the built-in WP_List_Table class.