L'amitié est une des choses les plus importantes du monde, surtout aujourd'hui - Friendship is one of the most important things in the world, especially today.
amitiés (at the end of a letter) - best wishes, all the best, kind regards, in friendship
Have you ever received a letter from a French friend signed "friendships"? This is a fairly common mistake by native French speakers. A more accurate translation of amitiés might be "your friend," but since that has a definite grade school sort of feeling, it's better to choose one of the translations above.
See amicalement for another, famous mistranslation by native speakers.
amitié particulière - homosexual relationship
prendre quelqu'un en amitié - to take a liking to someone
Faites-moi l'amitié de + infinitive... - Do me the kindness/favor of + gerund...
(click the little graphic below to hear the Mot du jour pronounced)