You can get a complete list of config.php overrides by placing the following code into any PHP-enabled template (input or output does not matter):
<pre>
<?php global $PREFS; print_r($PREFS); ?>
</pre>
Below is a full, outputted list for quick reference. Current as of 1.6.7:
$conf['enable_image_resizing'] = 'y';
$conf['image_resize_protocol'] = 'gd2';
$conf['image_library_path'] = '';
$conf['thumbnail_prefix'] = 'thumb';
$conf['word_separator'] = 'underscore';
$conf['use_category_name'] = 'n';
$conf['reserved_category_word'] = 'category';
$conf['auto_convert_high_ascii'] = 'y';
$conf['new_posts_clear_caches'] = 'y';
$conf['auto_assign_cat_parents'] = 'y';
$conf['strict_urls'] = 'n';
$conf['site_404'] = '';
$conf['save_tmpl_revisions'] = 'n';
$conf['max_tmpl_revisions'] = '5';
$conf['save_tmpl_files'] = 'n';
$conf['tmpl_file_basepath'] = '';
$conf['un_min_len'] = '4';
$conf['pw_min_len'] = '5';
$conf['allow_member_registration'] = 'y';
$conf['allow_member_localization'] = 'y';
$conf['req_mbr_activation'] = 'email';
$conf['new_member_notification'] = 'n';
$conf['mbr_notification_emails'] = '';
$conf['require_terms_of_service'] = 'y';
$conf['use_membership_captcha'] = 'n';
$conf['default_member_group'] = '5';
$conf['profile_trigger'] = 'member';
$conf['member_theme'] = 'default';
$conf['enable_avatars'] = 'y';
$conf['allow_avatar_uploads'] = 'n';
$conf['avatar_url'] = 'http://example.com/images/avatars/';
$conf['avatar_path'] = '/path/to/images/avatars/';
$conf['avatar_max_width'] = '100';
$conf['avatar_max_height'] = '100';
$conf['avatar_max_kb'] = '50';
$conf['enable_photos'] = 'n';
$conf['photo_url'] = 'http://example.com/images/member_photos/';
$conf['photo_path'] = '/path/to/images/member_photos/';
$conf['photo_max_width'] = '100';
$conf['photo_max_height'] = '100';
$conf['photo_max_kb'] = '50';
$conf['allow_signatures'] = 'y';
$conf['sig_maxlength'] = '500';
$conf['sig_allow_img_hotlink'] = 'n';
$conf['sig_allow_img_upload'] = 'n';
$conf['sig_img_url'] = 'http://example.com/images/signature_attachments/';
$conf['sig_img_path'] = '/path/to/images/signature_attachments/';
$conf['sig_img_max_width'] = '480';
$conf['sig_img_max_height'] = '80';
$conf['sig_img_max_kb'] = '30';
$conf['prv_msg_upload_path'] = '/path/to/images/pm_attachments/';
$conf['prv_msg_max_attachments'] = '3';
$conf['prv_msg_attach_maxsize'] = '250';
$conf['prv_msg_attach_total'] = '100';
$conf['prv_msg_html_format'] = 'safe';
$conf['prv_msg_auto_links'] = 'y';
$conf['prv_msg_max_chars'] = '6000';
$conf['memberlist_order_by'] = 'total_posts';
$conf['memberlist_sort_order'] = 'desc';
$conf['memberlist_row_limit'] = '20';
$conf['mailinglist_enabled'] = 'y';
$conf['mailinglist_notify'] = 'n';
$conf['mailinglist_notify_emails'] = '';
$conf['encryption_type'] = 'sha1';
$conf['site_index'] = 'index.php';
$conf['site_name'] = 'Site Name!';
$conf['site_url'] = 'http://example.com/';
$conf['theme_folder_url'] = 'http://example.com/themes/';
$conf['webmaster_email'] = 'youremail@example.com';
$conf['webmaster_name'] = '';
$conf['weblog_nomenclature'] = 'weblog';
$conf['max_caches'] = '150';
$conf['captcha_url'] = 'http://example.com/images/captchas/';
$conf['captcha_path'] = '/path/to/images/captchas/';
$conf['captcha_font'] = 'y';
$conf['captcha_rand'] = 'y';
$conf['captcha_require_members'] = 'n';
$conf['enable_db_caching'] = 'y';
$conf['enable_sql_caching'] = 'n';
$conf['force_query_string'] = 'n';
$conf['show_queries'] = 'y';
$conf['template_debugging'] = 'n';
$conf['include_seconds'] = 'n';
$conf['cookie_domain'] = '';
$conf['cookie_path'] = '';
$conf['user_session_type'] = 'c';
$conf['admin_session_type'] = 'cs';
$conf['allow_username_change'] = 'y';
$conf['allow_multi_logins'] = 'y';
$conf['password_lockout'] = 'y';
$conf['password_lockout_interval'] = '1';
$conf['require_ip_for_login'] = 'y';
$conf['require_ip_for_posting'] = 'y';
$conf['allow_multi_emails'] = 'n';
$conf['require_secure_passwords'] = 'n';
$conf['allow_dictionary_pw'] = 'y';
$conf['name_of_dictionary_file'] = '';
$conf['xss_clean_uploads'] = 'y';
$conf['redirect_method'] = 'redirect';
$conf['deft_lang'] = 'english';
$conf['xml_lang'] = 'en';
$conf['charset'] = 'utf-8';
$conf['send_headers'] = 'y';
$conf['gzip_output'] = 'y';
$conf['log_referrers'] = 'y';
$conf['max_referrers'] = '500';
$conf['time_format'] = 'us';
$conf['server_timezone'] = 'UM6';
$conf['server_offset'] = '';
$conf['daylight_savings'] = 'n';
$conf['default_site_timezone'] = 'UM6';
$conf['default_site_dst'] = 'n';
$conf['honor_entry_dst'] = 'y';
$conf['mail_protocol'] = 'mail';
$conf['smtp_server'] = '';
$conf['smtp_username'] = '';
$conf['smtp_password'] = '';
$conf['email_debug'] = 'n';
$conf['email_charset'] = 'utf-8';
$conf['email_batchmode'] = 'n';
$conf['email_batch_size'] = '';
$conf['mail_format'] = 'plain';
$conf['word_wrap'] = 'y';
$conf['email_console_timelock'] = '5';
$conf['log_email_console_msgs'] = 'y';
$conf['cp_theme'] = 'default';
$conf['email_module_captchas'] = 'n';
$conf['log_search_terms'] = 'y';
$conf['secure_forms'] = 'y';
$conf['deny_duplicate_data'] = 'y';
$conf['redirect_submitted_links'] = 'n';
$conf['enable_censoring'] = 'y';
$conf['censored_words'] = 'bad_words_go_here_separated_by_a_pipe|like_so';
$conf['censor_replacement'] = '###';
$conf['banned_ips'] = '';
$conf['banned_emails'] = '';
$conf['banned_usernames'] = '';
$conf['banned_screen_names'] = '';
$conf['ban_action'] = 'restrict';
$conf['ban_message'] = 'This site is currently unavailable';
$conf['ban_destination'] = 'http://www.yahoo.com/';
$conf['enable_emoticons'] = 'y';
$conf['emoticon_path'] = 'http://example.com/images/smileys/';
$conf['recount_batch_total'] = '1000';
$conf['remap_pm_urls'] = 'n';
$conf['remap_pm_dest'] = '';
$conf['new_version_check'] = 'y';
$conf['publish_tab_behavior'] = 'hover';
$conf['sites_tab_behavior'] = 'hover';
$conf['enable_throttling'] = 'n';
$conf['banish_masked_ips'] = 'y';
$conf['max_page_loads'] = '10';
$conf['time_interval'] = '8';
$conf['lockout_time'] = '30';
$conf['banishment_type'] = 'message';
$conf['banishment_url'] = '';
$conf['banishment_message'] = 'You have exceeded the allowed page load frequency.';
$conf['enable_search_log'] = 'y';
$conf['max_logged_searches'] = '500';
$conf['theme_folder_path'] = '/path/to/themes/';
$conf['is_site_on'] = 'y';
$conf['forum_trigger'] = 'forums';
$conf['app_version'] = '167';
$conf['license_number'] = '';
$conf['debug'] = '1';
$conf['install_lock'] = '1';
$conf['db_hostname'] = 'localhost';
$conf['db_username'] = '';
$conf['db_password'] = '';
$conf['db_name'] = '';
$conf['db_type'] = 'mysql';
$conf['db_prefix'] = 'exp';
$conf['db_conntype'] = '0';
$conf['system_folder'] = 'system';
$conf['cp_url'] = 'http://example.com/system';
$conf['doc_url'] = 'http://expressionengine.com/docs/';
$conf['cookie_prefix'] = '';
$conf['is_system_on'] = 'y';
$conf['allow_extensions'] = 'y';
$conf['multiple_sites_enabled'] = 'n';
$conf['forum_is_installed'] = 'y';
$conf['sc_paypal_account'] = '';
$conf['sc_encrypt_buttons'] = 'n';
$conf['sc_certificate_id'] = '';
$conf['sc_public_certificate'] = '';
$conf['sc_private_key'] = '';
$conf['sc_paypal_certificate'] = '';
$conf['sc_temp_path'] = '/tmp';
$conf['site_id'] = '1';
There are also some Hidden Configuration Variables.