A lot of Audiophiles, and more often just beat junkies, swear by Senn's headphones. Their product line, though, is a little light in the middle, where most people actually shop. Hence the HD 4x8 series, which graciously starts at $100.
There've been cheaper HD-branded models for years, and they've generally been pretty great. The $100 price point, though, marks sort of a golden zone for headphones and earbuds—it's the most a lot of people are willing to spend, and where the hardware starts to really shine. The HD 428, 438 (pictured above) and 448 sit in this $30 sweet spot, and fall somewhere between portable headphones and giant home stereo alien ear bulbs in terms of size.
The main differences between the headphones are sound signature—the cheaper 428 is bassier, while the 428 and 448 go for a more natural mix—and style—the 428 has a subdued cross pattern, the 448 a subtle brushed aluminum look, and the 438 has, er, hubcaps "reminiscent of the alloy wheels on luxury sports cars," by which Sennheiser presumably means 1984 Honda CRXes. Which is fine! [Sennheiser]