For earbuds at $50, Yuin PK3 is your best bet. Just got mine a few weeks ago, better than all those shitty ass Senny earbuds I've owned throughout the years. You have to be careful with them though as the quality isn't great apparently - sound is still good. Don't get Beats, mediocre sound for a fucking shitload of money. You'd rather get iPod ones (stay away from these fuckers)
over those pieces of shit.
Good portable headphones:
http://headphones.com.au/psingle?productID=19 Apparently amazing quality sound and make for portable headphones. Careful though, you may look like a douche.
For headphones, A-T AD700's are bang for buck. Probably your best bet for under $200. I would stay away from Sennheisser unless you go budget ones for $30 as those are better anything you'd get from Logitech.
If you're willing to spend big get Beyer Dynamics, heaps of vouches over the net for those. Should be worth it if you're willing to pay around $300-500.