Legal herbs will most likely leave you with a headache. I've never even heard of some of the "exotic" herbs they claim some indian tribe uses for extreme smoking pleasure.

24$ for a half ounce of plant material that cost cents to grow. BAH

If you want to get knocked on your ass try some homegrown tobacco. Native tobacco like Tobacco Alata and Tobacco Nicotinasomething will put you on the ground with one puff.