I'm going to Buenos Aires and i don't speak Spanish. Will i be able to get around the city on my own?

It depends on where you will be. If you stay in the city, especially the commercial and business sectors, you can always find people who speak English (or think they do LOL). Practically all museums and other tourist attractions are prepared for English-speaking people.
However, in other less touristic places it may be a little difficult. Don't worry, we're friendly people and you will find someone to help you :-)
Try to learn some basic phrases such as:
"No hablo espa帽ol" (I don't speak Spanish)
"驴D贸nde est谩 <place name>?" (Where is <>?)
"Muchas gracias" (thank you very much)
"Aguante Argentina" (Go Argentina) LOL well, the last one is just for an emergency :-P

Good luck!

yes...yes u will

Many southamerican people can speak english and they like to talk to foreigners in english to practise.
You will have no problem

If you are the typical US citizen who thinks every one MUST speak English, sure you'll find problems, if you make an effort to speak Spanish, which is very easy to learn and talk, maybe you'll have better luck!

There are alot of people in bsas that speak english or have an idea of it, but u shouldnt really count on someone speaking it.
Argentina is a great and beautiful country but its going threw a hard time and there are tons of people getting robbed and mugged. Being a tourist without the language really isnt a good idea. Expecially if u have an american passport. Most people will not want u arround.
I'll never forget one of the many times i went to argentina ( i am argentinian) close to the airport on the highway they had spray painted Yankee(american) go home.
Better go someone where, were u can speak the language.