I have the sony ex71. They are ok. they were my first decent phone. If you are just coming from stock phones, the immediate presence of bass is impressive. However, its weaknesses are soon apparent. Bass is too boomy and overshadow everything it seem.
From my own experiences with various phones and the forum, the forums has always been very accurate so I have no doubt the md33 are very good/better than the sony to most ears.
Never try the ety or shure, they are imo totally different class than sony. Sony is disposable, those you take good care of. I won' hestitate to just toss my sony into my bag, I will treat anything 60+ with more care.
I've been doing some research on the future sonic phone. I am somewhat tempted to get this... or one of AudioTechnica's clip on or their ear bud... sigh... There is not much about it here. There are some discussion. some place it somewhere between e3 and e5. They are also branded Sennheiser IE3.
http://futuresonics.umsebiz.com/stor...75&item=370255
at the very top end of your budget.
Never tried the koss, tho I was just at 3 of the radioshack stores around trying to find the koss 75
I do have the Senn 497 which is like 50-60 bucks and they are very nice. I do prefer my Audio Techinca a500 quite a bit, unfortunately, its a few bucks over the 100 dollar limit.
edit: It should be obvious that you are looking for portability

if so, disregard the headphones I mentioned, especially the a500