I'm looking at getting some new headphones and have about $100 to spend. My only requirements are that they are:

1. Over the ear headphones - preferably open
2. Comfortable for extended periods of use, especially while wearing glasses
3. Able to be driven decently by a portable cd player (~24 mW output)

I have been looking at Sennheiser HD570 but I hear they have trouble being powered by portable devices. I've also looked a little at the Grado sr80. Can I really go wrong with any sort of Sennheiser or Grado headphones? Are there any other good models or brands I should look at? I'm really interested in your personal experiences as I have no experience with anything more than cheap ~$30 headphones.

Edit: Anyone know anything about Beyerdynamic headphones? Specifically, I'm looking at the DTX900 model as a possibility.

Take a look at canalphones, they often aren't taken into consideration, but do have a lot of advantages and very good sound. There are threads on this topic at HA and even more at http://www.head-fi.org

Shure E2C for <100 price range.

Sennheiser HD555

The Grado SR80 are little short of amazing for the price.
But if you want to use them with a portale player, like many others, you really need a headphone amp.
Canalphones are the best for portable usage in this respect.
Dunno how much they cost near your place, but the Sennheisers 280 are excellent as well, probably better than the Grado SR80. I say "probably" because I tried them both several weeks apart from one another, so actual comparison is difficult.

Edit: forgive the spelling, I've slept 13 hours over the last 4 nights...