Anything can be portable. My sister has seen people walking around San Francisco listening to AKG K 701s and I even saw somebody walking down a sidewalk in Santa Monica wearing the AKG K 1000, though I'm not sure what it was connected to, if anything.
Just curious--do you know the difference between open & closed headphones? The DT 880 and all Grados (except their IEMs) are open, which means they will leak a lot of sound and will provide you with no isolation, either. If you do use one of those as a portable, just be careful not to annoy the people around you (e.g., on a bus, on a subway, or in a quiet area such as a library).
If you want a beyer, check out the DT 770 (it's closed) and if you're just going to be using it with an iPod or out of your laptop, pick the 32-ohm version. If you're willing to spend close to $300, you can even customize the look of the 770 on beyer's website before placing your order. Otherwise, the aforementioned Ultrasone and Audio-Technica models (from my previous post) should suit you very well for portable usage out of an iPod.
Edit: I agree with Ultrazino... You've definitely got a lot to learn. Seems like you're in a hurry to buy something, but seriously, there's enough information in these forums so you don't blow $300 on something that doesn't fit your needs.