Here is a list of things you can do to experience drug-like effects without actually taking any. The ways proposed here are (mostly) harmless and free!
* Stay awake for a long time. You will eventually hallucinate. (not so harmless)
* Go jogging. Free endorphin.
* Stand up really fast. You will experience a gentle black-out effect.

Any more suggestions?

* ''MentalStateCalledFlow''
* Sex. Love. Violence. Stroking cats. Eating anything. Not eating anything. Thinking. Breathing ...
* Motorcycling. Performance cars. Rollercoasters.
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Hyperventilation (nor harmless at all !)

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There's a wonderful book called "The Book Of Highs" which extols just these things. Written by Edward Rosenfeld, published by Quadrangle, ISBN 0812903293, but sadly now out of print.

From the back cover:

A whole consciousness catalog -- 250 ways to alter your consciousness without drugs. Methods, techniques, and ways involve:

''Just Yourself''

Concentration, sensory awareness, fervent prayer, alterations of breathing, self-hypnosis, meditation, voluntary silence, fantasy and daydreaming, remembering and reverie, myths, tales and koans, chanting and mantras, dreams applied to waking life, semantic awareness, running, nudity, ritual, sensory reminiscence, everyday experience.....

''Help from Others''

Psychoanalysis, self-analysis, gestalt therapy, sensory training, massage, hypnosis, encounter,
marathon, rolfing, compressed time, yoga, T'ai Chi Ch'uan, calligraphy and sumi, theatre games,
Gurdjieff, meher Baba, astrology, scientology, seance, orgasm, tantric sex, transcendental meditation, Buddhism......

''Devices and Machines''

Gliding, scuba diving, I Ching, bio feedback, continuous light and sound, psychedelic bathtub, Riley
room, moving moiré patterns, tarot, masks, negative ionization, hot and cold baths, land diving, sky
diving, skiing, engine rough, sensory deprivation, and many, many more.

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Can't help but say that's a lot of work for stuff most of us know how to accomplish far more effectively. :)

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Ever try sleeping? -- DonaldNoyes

''Hugging appropriate people, napping, sleeping (esp. in flannel sheets and pillows) is also a form of FreeDrugs. Dopamine and oxytocin are released, and many more.'' 
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A free high: Take your dog for a good long walk every day (or at least every other day) and you both will have lighter hearts and feel real fine!
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See also: FreeHugs