I would recommend the Grado SR60i. It is often talked about as the gateway drug to the high-end headphone world. Wonderful headphones and they are open, which means you can hear the outside world. Here's a link to a great headphone store: http://www.headphone.com/guide/by-manufacturer/grado/grado-sr-60i.php
I have some beyer DT331 which are over the ear open backed headphones. You can hear a lot with them on. Beyer do more expensive versions too. Lovely headphones.