Well, if you really want to join an organization, I suppose there's things like the IWW, Common Struggle, or RAAN (do they do official membership?). However, it sounds like you're fairly new to anarchism, and I would strongly recommend you figure out what anarchy means for you before you go and do something like that. If you want to meet other anarchists, try looking at your local scene first. Check out things like your local indymedia, infoshops, spaces, etc. Once you've been able to discuss things with friends for a while and test the waters of where you stand, you can come back to this sort of question - though at that point, there's a good chance you won't even need to come here for an answer.
