Absinthe was banned in the U.S. way back in 1912 because of it's famed hallucinatory effects. Well, makers of absinthe managed to find a loophole in the law. It seems that absinthe itself wasn't banned, but an ingredient called thujone, which what was thought to cause the effects. Turns out that even the old school brands of absinthe really didn't have that much thujone in them at all.
Through chemical analysis, makers found that the original brands of absinthe that caused it to become illegal had so little thujone in it that they would be considered legal by the letter of the law. After this fact was learned, all those modern bottles of honest to god absinthe (not some watered down or counterfeit version) that were illegal, turn out to be perfectly legal.
Since you can now buy absinthe anywhere that actually sells it, Esquire magazine has come up with the five best bottles you should go out and buy. You can view that list HERE.
There's a trick to drinking absinthe though, because the good stuff is usually 120 and 140 proof. The trick is to mix it with a little bit a sugar and some cold water. If you're not sure the best way to mix the drink, Esquire also has a how-to guide HERE.