Now i disagree with most folks here, there are some fantastic legal highs. GHB used to be legal, many designer hallicinogens are still legal, mescaline cactuses and a wide variety of fun plants like khat and many may more are all legal. Morning glory is legal (tho i wouldnt recommend it to evry1). Point is there are plenty of well established legal highs - most of these exist outside the commercial herbal high industry. Find out what the actives are and RESEARCH them. Ull prolly find that there are no true marijuana alternatives....why? because marijuana taps a rarely used and very specific part of the brain, canibanols are rare in nature.
Legal marijuana alternatives? maybe skullcap might make a lame relaxant. Nutmeg has some stoning properties but its mighty shit. Hops might be a go, its related to cannibis, but i doubt it gives you euphroria. Personally id forget it - and especially forget the idea of smoking alternatives - if we really found a tru alternative its quite likely it wouldnt be smokable...