[straygray]

I'm going to be getting some new headphones pretty soon. What do you guys think of Sennheiser HD555s versus Sennheiser HD428s?

 

[lilkoolaidman]

I assume you mean Sennheiser 428s? I have not heard the 555s but I have heard the 428s and didn't like them that much. The mids were pretty fake sounding and the bass was all over the place, and it wasn't even the kind of bass that makes the music fun. But that's me, if you have a local best buy near you, they carry the 428s and you can have a listen and decide for yourself.
 
The HD555s are full size and open, and can't really be driven from an iPod or portable media player (if that's what you're looking for). Also, the open nature of them means they are pretty much only useful for at-home headphones.
 
If you want portable headphones, some Sennheiser PX100s/PX100 ii (they're the same, I think), or some Koss Porta-Pros would be a great choice for around $50. They are very similar sounding with the Porta-Pros having slightly more bass and a little more recessed mids compared to the PX100s. Personally though, the Porta-Pros feel more durable to me. If you want bigger, full-sized, closed cans. The ATH-M50 cannot be beat for around $100, they aren't very portable but they do just fine running out of an iPod. Just make sure you get the coiled cable version instead of the ATH-M50-s (straight cable) since it has about an 8ft cable when straight, unless that's what you want.
 
These are just what I've heard, but you can do some research on other models by searching "best headphones under $100" here on Head-fi (there's a billion threads on that here)