This is my new plugin. Categories of your blog are shown on dashboard. By clicking the category you are going to write a post, you will go to a new post page, with the category checked.

When I make a new post, I often forget to check a category. This plugin solves the problem. Before I write a post, the category is already chosen. After I write a post, I simply push the publish button.

<?php
class selectcategory {

    protected $catid ;
    protected $js ;
    protected $number = 20;
    protected $hideempty = 0;
    protected $order = 'DESC';
    protected $unit = 'pt';
    protected $orderby = 'cloud';
    protected $maxnum = 22;
    protected $minnum = 8;

    public function __construct() {
        add_action( 'admin_head-post-new.php', array(&$this, 'catid_via_get') );
        add_action( 'wp_dashboard_setup', array(&$this, 'category_post_dashboard_widget') );
        add_action( 'admin_menu', array(&$this, 'myoptionpages_add') );
    }

    public function myoptionpages_add() {
        add_options_page(__('Select Category to Post', 'selectcategory'), __('Select Category to Post', 'selectcategory'), 'edit_plugins', 'selectcategoryoptions',  array(&$this, 'selectcategory_options_page') );
    }

    public function selectcategory_options_page() {
?>
<div class="wrap">
    <h2><?php _e('Options', 'selectcategory');?></h2>
<form method="post" action="options.php">
    <?php wp_nonce_field('update-options'); ?>
    <?php $selectcategory_order = esc_attr(get_option('selectcategory_order', 'count'));?>
    <table class="form-table">

        <tr valign="top">
            <th scope="row"><label for="selectcategory_num"><?php _e('Number of Categories', 'selectcategory');?></label></th>
            <td><input type="text" id="selectcategory_num" name="selectcategory_num" value="<?php esc_html_e(get_option('selectcategory_num', $this->number)); ?>" size="5"></input></td>
        </tr>
        <tr valign="top">
            <th scope="row"><label for="selectcategory_order"><?php _e('Order of Categories', 'selectcategory');?></label></th>
            <td><select id="selectcategory_order" name="selectcategory_order">
            <option value="name"<?php selected( $selectcategory_order, 'name' ); ?>><?php _e('Name','selectcategory'); ?></option>
            <option value="count"<?php selected( $selectcategory_order, 'count' ); ?>><?php _e('Count','selectcategory'); ?></option>
            <option value="none"<?php selected( $selectcategory_order, 'none' ); ?>><?php _e('term_id','selectcategory'); ?></option>			
            <option value="cloud"<?php selected( $selectcategory_order, 'cloud' ); ?>><?php _e('cloud','selectcategory'); ?></option>			
            </select></td>
        </tr>
         <tr valign="top">
            <th scope="row"><label for="selectcategory_order"><?php _e('Size of Clouds (if you choose cloud)', 'selectcategory');?></label></th>
             <td>Max: <input type="text" id="maxsize" name="selectcategory_maxnum" value="<?php esc_html_e(get_option('selectcategory_maxnum', $this->maxnum)); ?>" size="5"></input> &nbsp;&nbsp; min: <input type="text" id="minsize" name="selectcategory_minnum" value="<?php esc_html_e(get_option('selectcategory_minnum', $this->minnum)); ?>" size="5"></input></td>
        </tr>   </table>

    <input type="hidden" name="action" value="update" />
    <input type="hidden" name="page_options" value="selectcategory_num,selectcategory_order,selectcategory_maxnum,selectcategory_minnum" />

    <p class="submit">
    <input type="submit" class="button-primary" value="<?php _e('Save Changes', 'selectcategory') ?>" />
    </p>

</form>
</div>
<?php }

public function category_post_dashboard_widget() {
    wp_add_dashboard_widget('select_category_post', __('Select Category to Post', 'selectcategory'), array(&$this, 'select_category_post'));	
} 


    public function select_category_post() {
        $option_orderby = get_option('selectcategory_order', 'count');
        if ( $option_orderby == 'name' ) {
            $this->orderby = 'name';
        } elseif ( $option_orderby == 'cloud' ) {            
            $this->orderby = 'name';
        } elseif ( $option_orderby == 'count' ) {            
            $this->orderby = 'count';
        } elseif ( $option_orderby == 'none' ) {
            $this->orderby = 'none';
        } else {
            wp_die( 'invalid selectcategory_order' );
        }

        if ( is_numeric( get_option('selectcategory_num', $this->number) ) ) {
            $this->number = intval( get_option('selectcategory_num', $this->number) );
        } else {
            wp_die( 'invalid selectcategory_num' );	    
        }

        if ( $option_orderby == 'cloud' ) {
            print $this->output_cloudlist();
            } else {
            print $this->output_catlist();
            }
    }

   protected function output_cloudlist() {
        if ( is_numeric( get_option('selectcategory_maxnum', $this->maxnum) ) ) {
            $largest = intval( get_option('selectcategory_maxnum', $this->maxnum) );
        } else {
            wp_die( 'invalid selectcategory_maxnum' );	    
        }
        if ( is_numeric( get_option('selectcategory_minnum', $this->minnum) ) ) {
            $smallest = intval( get_option('selectcategory_minnum', $this->minnum) );
        } else {
            wp_die( 'invalid selectcategory_minnum' );	    
        }
        $categories = get_terms('category', array(
            'number' => $this->number,
            'hide_empty' => $this->hideempty,
            'orderby' => 'count',
            'order' => $this->order ));

        foreach ( $categories as $catdata ) {
                $counts[] = $catdata->count;
        }
         $min_count = min( $counts );
        $spread = max( $counts ) - $min_count;
        if ( $spread <= 0 ) {
            $spread = 1;
        }
        $font_spread = $largest - $smallest;
        if ( $font_spread < 0 ) {
            $font_spread = 1;
        }
        $font_step = $font_spread / $spread;

        uasort( $categories, create_function('$a, $b', 'return strnatcasecmp($a->name, $b->name);') );

            $output = "<ul class="selectcategory-cloud">n<li>n";
        foreach ( $categories as $catdata ) {
            $cat_id = $catdata->term_id;
            $catname = wp_specialchars( apply_filters('the_category', $catdata->name) );
            $output .= "<a href="" . admin_url('/') . "post-new.php?defaultcatid=". $cat_id ."" title="" . $catname . "" class="selectcategory-" . $cat_id . "" style='font-size: " . ( $smallest + ( ( $catdata->count - $min_count ) * $font_step ) ) . $this->unit . ";'>";
            $output .= $catname;
            $output .= "</a>n";
        }
            $output .= "</li>n</ul>n";
            
       return $output;
    }
    
   protected function output_catlist() {
        $categories = get_terms('category', array(
            'number' => $this->number,
            'hide_empty' => $this->hideempty,
            'orderby' => $this->orderby,
            'order' => $this->order ));

            $output = "<ul class="selectcategory">n<li>n";
        foreach ( $categories as $catdata ) {
            $cat_id = $catdata->term_id;
            $catname = wp_specialchars( apply_filters('the_category', $catdata->name) );
            $output .= "<a href="" . admin_url('/') . "post-new.php?defaultcatid=". $cat_id ."" title="" . $catname . "" class="selectcategory-" . $cat_id . "">";
            $output .= $catname;
            $output .= "</a>n";
        }
            $output .= "</li>n</ul>n";
            
       return $output;
    }
    
    public function catid_via_get() {
        if ( current_user_can('edit_posts') && is_numeric( $_GET['defaultcatid'] )){
            $this->catid = intval( $_GET['defaultcatid'] );
            $this->catidcheck() ;
        }  else  {
            $this->catid = 0;
        }
    }

    protected function catidcheck() {
        if ( $this->catid ) {
            add_action( 'admin_print_footer_scripts', array(&$this, 'output_js') );
        }
    }

    protected function create_js() {
        $this->js = <<<EOF
        <script>
window.onload= getcatid;
function getcatid(){
document.getElementById('in-category-
EOF;
        $this->js .= $this->catid;
        $this->js .= <<<EOF
').checked = true;
}  </script>
EOF;
    }

    public function output_js() {
        if ( get_cat_name( $this->catid ) ) {
            $this->create_js();  
            echo $this->js;
        } else {
            wp_die( 'invalid catid' );
        }
    }

}