Depends on how relaxed you want to get :)
Chamomile tea is known for is calming effects on the nerves and quieting effects on the chatty mind. Lavender is well-renowned for relaxation of body and mind. These two, alone or together, make a pleasant herbal tea that can help calm and relax without lulling you to sleep.
Hops (like in beer) is also known for it's calming, relaxing properties. I personally find hops to dull the senses as well, making it one of my least favorite herbs to sip if I'm planning on staying awake.
Although fragrant and herbal, chai teas usually use an actual tea base, meaning the tea contains caffeine - not the best for unwinding. In fact, all true teas - black, green, white, red, pu-erh, etc - will contain caffeine.
Celestial Seasoning's standard Sleepy Time tea has chamomile in it, but then throws in spearmint and lemongrass - a diuretic and a stimulant! So I wouldn't turn to it unless your idea of relaxing is dancing while holding your pee. (This explains their need to make a "Sleepy Time Extra" blend, the same misguided herbal concoction with sedative valerian root added in).
Speaking of valerian, this is the tea for relaxing you right to sleep, particularly valerian root tea. As a tea blender, I use valerian root with st. john's wort (a cheerful herb) and chamomile for the ultimate tea-k-o.
Another mother of a relaxing herb is kava-kava, known for it's superior anti-anxiety effects. It can be steeped, but I prefer to dissolve it's powder form in warm chocolate milk and down it like a shot in the evening (honestly, I don't know if anyone else in the whole world uses it this way.)
Looking for more? Look into kratom tea.
Hope this helps! Happy sipping :)
Lee @ Lee's Teas