I’ve been here for over a year now and I still use these on a daily basis (if only I had them when I first got here…)
http://www.comoviajo.com — Need to get somewhere and don’t know how? Just type in the addresses!
http://www.buenosairesherald.com — Don’t speak much castellano (local name for Spanish)? News in English!
Si ya sabés castellano, the two most popular diarios (the word periódico isn’t used here) are Clarín & La Nación.
As far as online dictionaries go, http://www.spanishdict.com is probably the most user-friendly.
Living here you will hear tons of words that you never learned in Spanish class. The local slang, lunfardo, is used by EVERYONE. I recommend these dictionaries: http://argentineslang.wordpress.com & El Portal del Tango.
OK, amigos. That’s enough to get you started. If I missed any good ones, leave them in the comments below!