再说 (zài shuō) has two uses: as a verb meaning 'to say again' or 'to postpone discussion'; as a conjunction meaning 'moreover, besides' — it is more colloquial and often used in speech to add a reason, while 并且 (bìng qiě) is more formal and written. 另外 (lìng wài) is also common but can be an adverb; 此外 (cǐ wài) is formal and used in lists.