For plane trips, I use a pair of Sennheiser HD-280s. They block out cabin noise really well and sound quite decent. My similarly priced Grados sound better, but don't block any sound whatsoever. And I'm not a big fan of sticking things in my ears, so "canalphones" are out.
I HATED the Koss Plugs. Sorry Alan. They are cheap, though.
For casual portable use (not air travel) I use a pair of Sony clip-ons (Sony MDR-Q22LP). Not audiophile, but better than ear buds, cheap, and durable (important for me).
