Do you mean listing the blogs alphabetically by their domain name?
If so, something like this should work;
global $wpdb;
$blogs = $wpdb->get_results( "SELECT * FROM {$wpdb->blogs} WHERE site_id = '{$wpdb->siteid}' ORDER BY domain ASC", ARRAY_A );
If you want to list the blogs alphabetically by the title defined in each blog's title (defined in Settings -> General), then you will have to loop over the above query results, and do a get_blog_option(blog_id, 'blogname'), save that result in an array (along with the blog's URL), then manually sort the array using PHP.
This could cause performance issues depending on the number of blogs you have though.