Weed.
I'm not trying to boast, act cool, or start any debates/arguments.
For me I find the best times are when I'm chilling with my friends and passing a few around. Everything becomes colorful and exciting, everyone becomes philosophers, and the only effects are a bad case of the giggles, a very hungry stomach, and a new ear to music.
I'm not a bum, or a stoner (well, maybe). I have my life in order, my priorities set, and I know my responsibilities. It isn't something that I rely on to be happy, it's just a good tool to help bring close relationships even closer.
Not to mention it makes even Taco Bell taste like the last fluffing supper.