The quad-core Xeons include the X5492 running on 150 watts at 3.4GHz, the X5470 needing 120 watts and running at 3.5GHz, and the X5430 needing just 50 watts at 2.66GHz. As for the dual-core Xeon X5270, it consumes 80 watts and has a clock frequency of 3.5GHz – the highest of Intel's Core line.
All three of the quad-core models are currently shipping, while the dual-core chip is expected to ship later this year. They won’t come in cheap, though. The high-end X5492 is $1493 and the X5430, the cheapest one, is $562.