Try the following:
User TSConfig restricts the user to a specified set of buttons; therefore, for access to all buttons without restriction, in User TSConfig, set: options.RTEkeyList = *
Page TSConfig adds the buttons required to edit the table and field you wish to edit; therefore, to add all buttons by default, in Page TSConfig, set RTE.default.showButtons = *
If you are trying to edit the bodytext field of a content element from table tt_content, then the TCA field types and palettes may specify a list of buttons to add; this specification takes precedence over RTE.default.showButtons ; to override any such setting in TCA for the bodytext field of table tt_content, in Page TSConfig, set RTE.config.tt_content.bodytext.showButtons = *
If you are trying to edit a text field from another table, then, in Page TSConfig, set RTE.config.tableName.columnName.showButtons = *
If you have not modified $GLOBALS['TYPO3_CONF_VARS']['EXTCONF']['rtehtmlarea']['HTMLAreaPluginList'], all buttons should now be displayed (except perhaps the spellchecker button if some requirements are not met).