Not a doctor, so this is just the insight of an herbalist. This is not medical advice, I'll just tell you my own experience.
St. John's Wort is an herb that has been used historically to treat depression. I use it myself, and am a fan of its cheerful effects. Instead of sitting around full of anxiety wondering what I should be doing, or what I might be forgetting, I find myself sitting around thinking "hey, everything's alright." I drink it as a tea - here's how to prepare it: http://hubpages.com/food/Brewing-Herbal-Tea-How-to...
Kava kava is an herb I use to curb my urge to drink alcohol at night. It helps quell my need to want more, or want different, and helps me be ok, even feel good, about right now. I buy it ground up and drink 1 Tbsp mixed with warm chocolate milk. It's grainy, thick, and makes your tongue a little numb. It tastes pretty bad, but the effects are pleasant bordering on euphoric.
Ginkgo biloba is an herb that helps with mental function and memory recall. When my mind is feeling sluggish or I'm getting frustrated with tasks in my day, Ginkgo tea helps get me back on my game. I steep 1 tsp. in 1 cup hot water for 5 minutes.
Eleuthero root (aka siberian ginseng) helps with physical stamina and energy. I steep 1 tsp to 1 cup of hot water for 5-10 minutes. I make a tea with both ginkgo and ginseng, you can find that here: https://www.etsy.com/listing/114998632/organic-her...
Getting into the more exotics, kratom is an herb that mimicks the effects of an opiate without being one. It can seriously downshift your mental and physical activity, but I find it comes with a moderate amount of anxiety.
I understand bipolar symptoms can range extreme along a "manic/depressive" spectrum. So for me, I would treat symptoms individually as they come. My mother is a manic depressive bipolar schizophrenic that has been on pharmaceuticals for over 20 years. If she could be stable without them I'd have some teas for her to try...but weaning her off her medication has not proven successful, and I foresee she'll need them throughout the rest of her life. Even still, she likes my chamomile, lavender, and peppermint teas for gentle relaxation. My shop makes aromatherapy sprays too, body and pillow sprays, specifically designed to relax, rest, release, and renew. My business stems from my desire to help others like my mom naturally - maybe it can help you :)