The list is available in
$GLOBALS['l10n'][ $text_domain ].
To get the looong list of translatable WordPress strings just use:
print '<pre>' . htmlspecialchars( print_r( $GLOBALS['l10n']['default'], TRUE ) ) . '</pre>';
Do not use these strings in your theme or plugin.
They are internal, de facto private. They can change any time, even in minor updates. Always use your own strings only, even when you think: this was stable for years!
HTML tab in the post editor has been renamed to
Text. I wonder how many plugins will break now … :)