You should consider joining affiliate programs to mailing list promote products that are relevant to the content of your newsletter. Relevancy is a key factor here; otherwise you won't only not make sales but you might also lose mailing list valuable subscribers. Similarly, be sure of the products you are promoting and try as much as possible to give unbiased review or editorial. Sometimes.
It would be a good idea to try out the product first before promoting it to your mailing list. If it is a good product you will definitely mailing list recoup your investment many times over. However, where you can't try the product first; don't just rely solely on the review of the merchant's promotional materials provided to you. You should Googled and research for other affiliate's review and compare notes to come up with your own unique review.
As your mailing list keep on growing, you should consider selling ad space to other marketers that are in niches related to yours. You must not accept ads that are in direct competition with your own or the affiliate products you are promoting. Rather the ads mailing list should complements whatever products you are promoting. Banners and classified adverts come into minds here.