S-Adenosyl methionine. Its a supplement that is naturally produced by your body, has no side effects and acts as an anti-depressant. Some studies have shown that it is equal in efficacy to regular anti-depressants. There have been warnings against taking this if you are manic and with MAOI’s and SSRI’s due to Serotonin Syndrome (too much serotonin which causes problems) but with the SSRI’s I think you can do it if you are careful. The FDA’s take on that part has been refuted in literature saying that 700,000 people take this with anti-depressants and it is helpful for them.
Another one that is talked about that is similar but hasn’t gained as much acceptance from the scientific community is 5HTP.
You can read reviews on them through Google or at products on Amazon.