Koss Porta Pro Very good portable headphones for the price. Great bass response even from weak portable sources, excellent for listening to movies when travelling.
Koss Pro 4AAT Titanium These are difficult to describe. They have a superb amount of isolation and a good frequency response. I really like them, and they are my favourites for rock music and classical. They don't quite have the bass response of the Sony MDR-XB700.
Sony MDR-XB700 These are very much a "fun" headphone. A ridiculous amount of bass response, but they are lacking in isolation and they also have a recessed mid-range which makes rock music sound not so great and very bloated, but this can be fixed with a little EQ fiddling. Anything bassy sounds awesome on these headphones (e.g. rap), especially when powered from an amp.
Sennheiser CX500 These again have quite a bloated, bassy sound signature. They are suitable for listening un-amped to portable sources. Theu lack the clarity of the Ultimate Ears.
Ultimate Ears SuperFi 5 When I first got these I hated them. I thought I had wasted my money. Using an amp, and a little EQ "fixed" them however, and I now really enjoy them. They don't have the bass response of the CX500s but they do everything else much better.