Yerba Mate
Honestly, I think Yerba Mate is probably the most pleasant and cleanest caffeinated beverage around. I've pretty much entirely replaced coffee at this point, as Yerba Mate seems to have all around superior effects. The unique blend of methylxanthine stimulants present (caffeine, theobromine, theophylline) in Mate provides incredibly clean stimulation with no crash and little anxiety (for me anyway). It doesn't make my stomach feel nasty after multiple cups, which I appreciate as well. The guayaki canned drinks initially got me into it, but I've since graduated to brewing the unsmoked loose leaf tea.
Personally, I prefer the unsmoked varieties of the loose leaf tea (although it is traditionally smoked). I do however prefer the traditional cut, which includes the stems and makes it less bitter. I get the "Eco Teas" brand, just because it seems to be available at one of the local, ritzy grocery stores. There are a million brands out there, I've only tried a few. Guayaki sells their loose leaf Mate at whole foods, but I have not tried it myself. I think the canned drinks are a good place to start to see if you like the effects, they just have a significant amount of sugar in them.