540 is very good for peak season travel. Normally it would be closer to $1000, but this summer has yielded some real bargains on transatlantic flights. London has not usually been coming up cheapest in my price searches for this summer (probably due to the very high taxes in flights in/out of the UK), so 540 is probably as good as you’ll get. Just to be sure, check BookingBuddy.com as well as consolidators Cheapflights.com, Tiss, Airdeals, Justfares, and EconomyTravel.com.

Have you considered looking for an open-jaw ticket (e.g. fly into London, come home from Milan)? It might cost a little more for the initial ticket but you won’t have to pay to get back to London and you won’t waste a day backtracking. Look for open-jaw fares that pair two of your cities and see what you can find. I posted a couple of examples below.. Also, are you completely set on going to Milan? Most people here, myself included, recommend skipping it.

$558 Newark-Barcelona, Berlin-JFK bookable on Vayama.com once you deselect the optional travel insurance (or$591 on Delta’s website) for 7/21-8/14

$637 Newark-Vienna, Berlin-JFK bookable on nwa.com 7/22-8/16. This would allow you to do the same circuit you originally planned, just in a different order.

Wow those are some really good prices!
And also, I had no idea about the open-jaw tickets. To be frank, I didn’t even know they existed. I’ll have to go snooping around the net more.
And yes, I have to go to Milan because a friend of mine lives there, that way I save up on housing costs. But, where else do you guys recommend going?
I am still quite new in this whole thing so any new recommendations and advices will be greatly appreciated!!

Another option I saw is Newark to Berlin, Vienna to Newark 7/21-8/16 on SAS for $612. You can book on SAS.com. You could start in Berlin and go counter clockwise to visit the cities you originally planned on seeing.