A press release from Response Source brought to my attention an article from PR Workshop that says:

A clinical trial shows without a doubt that a herbal supplement comprising 450mg St John's Wort (Hypericum perforatum) and 350mg Passionflower (Passiflora incarnata) per daily dose can ease mild to moderate depression. Significantly it shows a considerable reduction in depression and anxiety. The results were felt quickly - within two weeks of taking the supplement (St John's Wort alone is recognised as achieving this reduction within four to six weeks).

I'm always a bit eery about using herbal remedies because of the lack of controls. Unlike prescription medications, they aren't FDA approved and haven't been clinically tested. I worry about impurities and a variant in the strength of the medicinal herbs.

However, this time there seems to have been clinical trials using controls and a placebo. There's even an email address given where you can find out more about it:
Katherine@prworkshop.co.uk

The Science Blog agrees that St. John's Wort is good for depression:

Hypericum (St.John's Wort) is a plant that has been used for centuries as a medicinal herb. Experimental studies show that hypericum has antidepressant properties in animal models of depression. Furthermore the mechanism by which this antidepressant effect is exerted has been shown to be similar to many standard antidepressants. Supporting the pre-clinical studies, a number of clinical studies have shown that hypericum is an effective antidepressant for the treatment of mild to moderate depression.