Also, would the Sennheiser's work as noise canceling headphones? Can someone sitting next to me hear the music?
The 555 and 595s are open phones. They're basically giant speakers attached to your head. People around you will hear everything you hear, and you will hear everything around you (like the people telling you to turn it down!). If you need isolation, your best bet are IEMs or canalphones.
"Noise-canceling" phones aren't nearly as good, because they simply add noise to what you're listening to in order to cancel out the noise you don't want to hear. It's inefficient, and it lowers sound quality, because the sounds added take away from whatever you're trying to listen to.
Canalphones, on the other hand, are basically earplugs with tiny speakers embedded in them. With those, you can play your music at much lower volumes, because they form a seal between you and the outside world, enabling you to listen as quietly or as loudly as you want without disturbing others, or being disturbed by your surroundings.
A good pair of Canalphones are the Creative EP-630s. I use them, and the sound quality is great. Many people also like the Sennheiser CX-300s. Regardless, remember that the Sennheisers above are open phones, which means zero isolation. That also applies to every Grado phone in existence, if you're considering those too.
As an Amazon Associate, MacRumors earns a commission from qualifying purchases made through links in this post.