Weed
It is the ultimate non-physically addictive happy grass that makes things like sex, food, tv, music and driving so freaking awesome. Weed helps with my seasonal depresion better than any prescription drug and unlike prescription anti-depressants doesn't build physical dependancy. It also works almost instantly, unlike the drugs so my blues is gone within 5 mins of me taking a couple of hits. Weed is my ultimate drug of choice.
Abusing herb (smoking out the whole day, every day hehehe...) CAN  have a bit of mental dependency, but no major effects if you go without it. Also NOT smoking, or taking a break for about a couple of days will actually make you feel more energetic and appreciate how weed doesnt affect you permanently. To all the people who knock on weed and then go and smoke cigarettes and drink alcohol -- you're all a bunch of hypocrites! (P.S. Gandalf and the hobbits smoke that "Shire weed" hahaha)