As for brands of absinthe, two stand out in my opinion: Lucid Absinthe from Hood River Distillers in Oregon is very nice. Also the absinthe vert from Ridge Distillers (I think they are called Vilya Spirits now) is good. They also make a very anise-forward gin if that's your thing.
If you can find it (or purchase from overseas) Verte de Fougerolles 72 is in my opinion fantastic and a good example of a traditional recipe. It's bitter, clean taste requires a sweetener to balance and the color is not fixed and can appear a bit muddy. Some complain of a grassy note but I love it.
The compound of concern as a few here have noted is in fact thujone. The TTB requires absinthe (or for that matter any distilled spirit) to be "thujone free" which oddly enough is 10 PPM.
Also, as others have noted here, the thujone comes from both grand (used in the maceration step) and petite wormwood (used in coloring step). It was never the thujone that provided the halicinatory effects, bur rather the fact that absinthe is generally bottled at above 70% abv and (unfortunately) immensely drinkable.
Although not especially difficult to make (expensive yes, difficult no), anyone who purchases an "absinthe herb kit" from their LHBS shop and simply soaks them in a purchased spirit will be in for an unpleasant experience.
Edit: Spelling