the most expensive does not always equal the best. as far as what's available in the U.S., that's a crap shoot as well. i live in wisconsin and my selection is very limited and i usually do all my purchases online. always look for the words "100% agave" on the label. some of my favorites are:
don julio 1942 (about $110 - $115 US but i just scored one for $89)
buscadores (in the $40's)
asom broso (in the $100's)
corazon (in the $30's)
casa noble (in the $50's)
the prices are ballpark figures for anejo or reposado, i tend not to like sipping the blanco's. as a side note, i just opened my first 1942 this weekend and it is magnificent!!!
some of the others recommended to me that i plan on buying on my trip to mexico in october:
jose cuervo reserva familia
arette - gran clase
i am by no means an authority on tequila. i've been reading all i can for the last 2-3 years and frequent several message boards to continue learning.